U.S. patent application number 13/696590 was filed with the patent office on 2013-09-19 for fin for surf craft.
This patent application is currently assigned to FIN CONTROL SYSTEMS PTY. LIMITED. The applicant listed for this patent is Michael James Durante, Gregory John Scott. Invention is credited to Michael James Durante, Gregory John Scott.
Application Number | 20130244514 13/696590 |
Document ID | / |
Family ID | 44991077 |
Filed Date | 2013-09-19 |
United States Patent
Application |
20130244514 |
Kind Code |
A1 |
Scott; Gregory John ; et
al. |
September 19, 2013 |
FIN FOR SURF CRAFT
Abstract
A fin (410) with a discrete structural strand layer (420) that
may include high tensile carbon fibre strands (422, 424) and high
tensile strength and toughness Kevlar (426) strands. These
structural strands may have a tensile strength substantially
greater than the other materials typically used in a fin body. The
structural strand layer (420) provides an economic and ready
technique to vary and control a stiffness characteristic of the fin
in a variety of directions or about a variety of axes of rotation;
without varying the other common components that may be used in a
fin body, for example core (412), layers of fibreglass fabric (414)
and/or resin.
Inventors: |
Scott; Gregory John; (New
South Wales, AU) ; Durante; Michael James; (New South
Wales, AU) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Scott; Gregory John
Durante; Michael James |
New South Wales
New South Wales |
|
AU
AU |
|
|
Assignee: |
FIN CONTROL SYSTEMS PTY.
LIMITED
New South Wales
AU
|
Family ID: |
44991077 |
Appl. No.: |
13/696590 |
Filed: |
May 17, 2011 |
PCT Filed: |
May 17, 2011 |
PCT NO: |
PCT/AU2011/000569 |
371 Date: |
May 16, 2013 |
Current U.S.
Class: |
441/79 ;
264/257 |
Current CPC
Class: |
B63B 32/60 20200201 |
Class at
Publication: |
441/79 ;
264/257 |
International
Class: |
B63B 35/79 20060101
B63B035/79 |
Foreign Application Data
Date |
Code |
Application Number |
May 17, 2010 |
AU |
2010902123 |
Claims
1. A fin for surf craft comprising: a fin body; and at least one
layer of structural strands, located within the fin body; wherein
the structural strands are in one or more non-woven arrangements;
and the structural strands have a physical property greater than a
corresponding physical property of other material forming the fin
body; and wherein the physical property is selected from at least
one of a toughness, a tensile strength, an elastic moduli and a
Youngs modulus.
2. A fin according to claim 1, wherein the fin comprises a base
portion and a tip portion and at least a portion of the structural
strands extends substantially from the base portion to the tip
portion of the fin.
3. A fin according to claim 1, wherein the fin comprises a base
portion and a leading edge portion and at least a portion of the
structural strands extends substantially from the base portion to
the leading edge portion of the fin.
4. A fin according to claim 1, wherein the fin comprises a leading
edge portion and a trailing edge portion and at least a portion of
the structural strands extends substantially from the leading edge
portion to the trailing edge portion of the fin.
5. A fin according to claim 1, wherein the fin comprises opposing
faces and at least one layer of structural strands in one or more
arrangements is located within the fin body such that the at least
one layer of structural strands is substantially parallel to the
opposing faces of the fin.
6. A fin according to claim 1, wherein the structural strands of at
least one layer are substantially parallel to each other.
7. A fin according to claim 6, wherein the fin comprises a sweep
angle and, in a first arrangement, the substantially parallel
structural strands are generally parallel to the sweep angle of the
fin.
8. A fin according to claim 6, wherein the fin comprises a sweep
angle and, in a first arrangement, the substantially parallel
structural strands are at a first angle to the sweep angle of the
fin, the first angle being in the range of up to 20 degrees.
9. A fin according to claim 8, the first angle is approximately 10
degrees.
10. A fin according to claim 6, wherein, in a second arrangement
the substantially parallel structural strands are at a second angle
to the vertical of the fin, the second angle being in the range of
20 to 40 degrees.
11. A fin according to claim 6, wherein the fin comprises a
vertical component and, in a second arrangement, the substantially
parallel structural strands are at an angle of approximately 30
degrees to the vertical of the fin.
12. A fin according to claim 6, wherein, in a third arrangement,
the substantially parallel structural strands are generally
vertical.
13. A fin according to claim 6, wherein the fin comprises a sweep
angle and, in a primary arrangement, the substantially parallel
structural strands are generally perpendicular to a sweep angle of
the fin.
14. A fin according to claim 13, wherein, in a secondary
arrangement, the substantially parallel structural strands are at a
first angle to a sweep angle of the fin, the first angle being in
the range of 20 to 40 degrees.
15. A fin according to claim 13, wherein, in a secondary
arrangement, the substantially parallel structural strands are at a
first angle of approximately 30 degrees to a sweep angle of the
fin.
16. A fin according to claim 13, wherein, in a tertiary
arrangement, the substantially parallel structural strands are
generally vertical.
17. A fin according to claim 1, wherein at least one layer of
structural strands comprises of a plurality of structural strands
extending from at least one substantially common point in a
substantially radial formation.
18. A fin according to claim 17, wherein the fin comprises a base
portion and the at least one substantially common point is adjacent
the base portion of the fin.
19. A fin according to claim 17, wherein the fin comprises a
leading edge portion and a trailing edge portion and the at least
substantially common point is adjacent at least one of a leading
edge portion and a trailing edge portion of the fin.
20. A fin according to claim 1, wherein at least one structural
strand comprises of a plurality of filaments.
21. A fin according to claim 1, wherein at least one structural
strand is made of at least one of carbon fibre, Kevlar, aramide,
natural fibres and synthetic fibres.
22. A fin according to claim 1, wherein at least one structural
strand has a tensile strength that is at least 1.5 times greater
than the tensile strength of the other material forming the fin
body.
23. A fin according to claim 1, wherein at least one structural
strand has a Youngs modulus that is at least 1.5 times greater than
a Youngs modulus of the other material forming the fin body.
24. A fin according to claim 1, wherein at least one structural
strand has a toughness that is greater than a toughness of the
other material forming the fin body.
25. A fin according to claim 1, wherein at least a portion of the
structural strands comprises unidirectional filaments in a ribbon
configuration.
26. A fin according to claim 1, wherein at least a portion of the
structural strands have a width in the range of 0.5 to 3 mm.
27. A fin according to claim 1, wherein at least a portion of the
structural strands has a width in the range of 1 2 mm.
28. A fin according to claim 1, wherein at least a portion of the
structural strands comprises of at least about 3,000 filaments per
structural strand.
29. A fin according to claim 1, wherein the fin comprises a base
portion and a tip portion and a spacing between at least a portion
of the structural strands is less towards the base portion compared
with the tip portion of the fin.
30. A fin according to claim 1, wherein a spacing between at least
a portion of the structural strands is in the range of 1 to 30
times a width of one structural strand.
31. A fin according to claim 30, wherein a spacing between at lest
a portion of the structural strands is in the range of 4 to 13
times a width of one structural strand.
32. A fin according to claim 1, wherein a spacing between at least
a portion of the structural strands is in the range of 4 to 15
mm.
33. A fin according to claim 32, wherein a spacing between at least
a portion of the structural strands is in the range of 9 to 13
mm.
34. A fin for surf craft comprising: a fin body; and at least one
layer of structural strands, located within the fin body; wherein
the structural strands are in one or more woven arrangements that
are at least one of an open weave and a scrim; wherein the
structural strands have a physical property greater than a
corresponding physical property of other material forming the fin
body; and wherein the physical property is selected from at least
one of a toughness, a tensile strength, an elastic moduli and a
Youngs modulus.
35. A fin according to claim 34, further including a core structure
located within the fin body.
36. A fin according to claim 35, wherein at least one layer of
structural strands in one or more arrangements is embedded within a
body of the fin such that the layer of structural strands is
substantially parallel to a face of the core structure.
37. A fin according to claim 35, wherein the fin comprises opposing
faces and the at least one layer of structural strands are located
intermediate the core structure and at least one of the opposing
faces of the fin.
38. A fin according to claim 35, wherein the core is at least one
of a foam core structure and a solid, non-foam core structure.
39. A fin according to claim 35, wherein at least a portion of the
core structure is made of at least one of PVC foam, polyurethane
foam, resin impregnated fibreglass, hardened resin, polyester mat,
microspheres, plastic, bamboo and wood.
40. A fin according to claim 34, wherein the fin body comprises a
base portion and further includes at least one layer of
unidirectional carbon fibre fabric towards the base portion of the
fin body.
41. A fin according to claim 40, wherein the at least one layer of
carbon fibre fabric is located about a periphery of the fin
body.
42. A fin according to claim 34, having a sweep angle of from 20 to
60 degrees.
43. A method of controlling a fin physical property for a surf
craft, the method comprising: selecting one or more structural
strands having a structural strand physical property greater than a
corresponding physical property of other materials in a body of the
fin; selecting a number of structural strands to provide the fin
physical property; providing a layer of the structural strands in
one or more arrangements; and embedding the layer of structural
strands in the body of the fin; whereby varying at least one of the
structural strands selection, the number of structural strands or
the arrangement of the structural strands varies the fin physical
property; and wherein the fin physical property is selected from at
least one of: a stiffness characteristic, a bending resistance, a
twisting resistance, a resistance to a deflection, a flexibility
and a high elastic recoil; and wherein the structural strand
physical property is selected from at least one of: a toughness, a
tensile strength, an elastic moduli and a Youngs modulus.
44. A method according to claim 43, wherein the step of providing a
layer of structural strands includes the use of a template to
locate one or more structural strands of one or more
arrangements.
45. A method according to claim 44, wherein the step of using a
locating template further includes providing at least one of pins,
adherents and securing systems to locate one or more structural
strands.
46. A method according to claim 44, wherein the step of using a
locating template further includes the steps of: providing one or
more reliefs machined into the template, and laying individual
structural strands into respective reliefs to form a three
dimensional structural strand layer.
47. A method according to claim 44, wherein the step of providing a
layer of structural strands includes the use of a numerically or a
computer controlled machine to locate one or more structural
strands of one or more arrangements.
48. A method according to claim 43, wherein the step of providing a
layer of structural strands further includes a step of: configuring
the arrangement of structural strands in a layer to vary the fin
physical property.
49. A method according to claim 43, further including providing one
or more structural strands largely parallel to a sweep angle of the
fin such that the fin is provided with an increased resistance to a
twisting of the fin.
50. A method according to claim 43, further including providing one
or more structural strands at a first angle of up to 20 degrees to
a sweep angle of the fin to provide the fin with an increased
resistance to a twisting of the fin.
51. A method according to claim 43, further including providing one
or more structural strands at a second angle in the range of 20 to
40 degrees to the vertical axis of the fin such that the fin is
provided with an increased resistance to a deflection from the
vertical axis
52. A fin for surf craft produced according to the method of claim
43.
53. (canceled)
54. (canceled)
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to fins and methods for making
them as may be applied to surf craft such as surfboards,
windsurfers, paddleboards, wave and surf skis, kite-boards, wake
boards and the like.
[0003] 2. Description of the Art
[0004] Surf craft (including surfboards) often have one or more
fins located on an underside of the surf craft that, for example,
may be used for stability, controlling direction and facilitating
turning of the surf craft. In addition surfboards may have multiple
fins with different functions, for example an uppermost side fin
with a curved or airfoil profile may function so as to provide to
provide lift when the surfboard is travelling across the face of a
wave and the uppermost side fin is located within the face of the
wave. It also follows that extra acceleration and drive to the
surfboard results.
[0005] Fin/s of turning surf craft may experience substantial side
ways and other forces to the face of the fin/s. How the fin/s
respond to these sideways and other forces in turns and other
manoeuvres may strongly affect the performance of the surf craft
for a particular set of surf conditions. The construction of a fin
may in particular affect its response to sideways and other forces
in use.
[0006] Current surfing trends, particularly in competitive surfing,
involve multiple, high speed, sharp turns of a surfboard whilst a
wave is being ridden. Such manoeuvring of a surfboard places very
significant forces on the fins of the surfboard. Under such forces,
the fins tend to experience bending (e.g. between the base and the
tip of the fin) and twisting (e.g. between the leading and trailing
edges of the fin). The fin's ability to return sharply to its
normal state following the removal of the experienced force (e.g.
via a turn) affects the performance of the fin and, consequently,
the surfboard.
[0007] Commonly available fins for surfboards may be a composite
structure of layers of bi-directional fibreglass fabric imbedded in
a suitable resin and then moulded and/or shaped to the form of a
fin. The word "bi-directional" in the following is taken to include
the direction of the fibreglass strands within the closely woven
fabric. The fibreglass strands being often made up of multiple
fibres or filaments of fibreglass. Bi-directional fibreglass or
other reinforcing fabric often has a basket weave pattern where the
strands are closely interwoven orthogonally to form the fabric.
[0008] The reinforcing fibreglass fabric together with the
impregnating resin or other suitable material typically determines
the physical properties of the fin in terms of, by way of example,
the stiffness characteristics, bending resistance, twisting
resistance and/or flexibility of the fin to sideways and other
forces in a turn or other manoeuvres. However for typical fins,
varying the stiffness characteristics, flexibility or other such
properties of the fin in an easily manufacturable and controllable
fashion is difficult due to the many layers of reinforcing fabric
with impregnating resin matrix contributing to the stiffness or
flexibility across the fin. There is also the additional limitation
of what is commercially available in reinforcing fabrics and the
strand materials forming them.
[0009] None of these prior art fin devices and methods of
construction for fins provides an entirely satisfactory solution to
the provision of fins for surf craft where the desired stiffness
characteristics and other physical properties may be varied in a
controllable fashion, nor to the ease of providing a convenient and
reliable way of manufacturing fins having different degrees of
stiffness or other desirable physical properties.
SUMMARY OF THE INVENTION
[0010] The present invention aims to provide an alternative method
for constructing a fin in which the stiffness characteristics and
other physical properties of the fin may be better controlled
and/or varied as well as to the provision of fins with different,
controlled stiffness characteristics which overcomes or ameliorates
the disadvantages of the prior art, or at least provides a useful
choice.
[0011] In one form, the invention provides a fin for surf craft
comprising: a fin body and at least one layer of structural
strands, located within the fin body; wherein the structural
strands are in one or more non-woven arrangements; and the
structural strands have a physical property greater than a
corresponding physical property of other material forming the fin
body; and wherein the physical property is selected from at least
one of a toughness, a tensile strength, an elastic moduli and a
Youngs modulus. Preferably at least a portion of the structural
strands extend substantially from a base portion to a tip portion
of the fin. Preferably at least a portion of the structural strands
extend substantially from a base portion to a leading edge portion
of the fin. Preferably at least a portion of the structural strands
extend substantially from a leading edge portion to a trailing edge
portion of the fin. Preferably at least one layer of structural
strands in one or more arrangements is located within the fin body
such that the at least one layer of structural strands is
substantially parallel to opposing faces of the fin.
[0012] Preferably the structural strands of at least one layer are
substantially parallel to each other. Preferably in a first
arrangement, the parallel structural strands are generally parallel
to a sweep angle of the fin. In an alternate first arrangement, the
parallel structural strands are at a first angle to a sweep angle
of the fin, the first angle being in the range of up to 20 degrees,
more preferably the parallel structural strands are at a first
angle of approximately 10 degrees to a sweep angle of the fin.
Preferably a second arrangement the parallel structural strands are
at a second angle to the vertical of the fin, the second angle
being in the range of 20 to 40 degrees more preferably the parallel
structural strands are at a second angle of approximately 30
degrees to the vertical of the fin. Preferably a third arrangement,
the parallel structural strands are generally vertical.
[0013] Preferably in a primary arrangement, the parallel structural
strands are generally perpendicular to a sweep angle of the fin.
Preferably in a secondary arrangement, the parallel structural
strands are at a first angle to a sweep angle of the fin, the first
angle being in the range of 20 to 40 degrees, more preferably the
parallel structural strands are at a first angle of approximately
30 degrees to a sweep angle of the fin. Preferably in a tertiary
arrangement, the parallel structural strands are generally
vertical.
[0014] Preferably at least one layer of structural strands
comprises of a plurality of structural strands extending from at
least one substantially common point in a substantially radial
formation. Preferably at least one substantially common point is
adjacent the base portion of the fin. Preferably at least
substantially common point is adjacent at least one of a leading
edge portion and a trailing edge portion of the fin.
[0015] Preferably at least one structural strand comprises of a
plurality of filaments. Preferably at least one structural strand
is made of at least one of carbon fibre, Kevlar, aramide, natural
fibres and synthetic fibres. Preferably at least one structural
strand has a tensile strength that is at least 1.5 times greater
than the tensile strength of the other material forming the fin
body. Preferably at least one structural strand has a Youngs
modulus that is at least 1.5 times greater than a Youngs modulus of
the other material forming the fin body. Preferably at least one
structural strand has a toughness that is greater than a toughness
of the other material forming the fin body. Preferably at least a
portion of the structural strands comprises unidirectional
filaments in a ribbon configuration. Preferably at least a portion
of the structural strands have a width in the range of 0.5 to 3 mm.
Preferably at least a portion of the structural strands has a width
in the range of 1 to 2 mm. Preferably at least a portion of the
structural strands comprises of at least about 3,000 filaments per
structural strand.
[0016] Preferably a spacing between at least a portion of the
structural strands is less towards the base portion compared with
the tip portion of the fin. Preferably a spacing between at least a
portion of the structural strands is in the range of 1 to 30 times
a width of one structural strand, more preferably a spacing between
at least a portion of the structural strands is in the range of 4
to 13 times a width of one structural strand. Preferably a spacing
between at least a portion of the structural strands is in the
range of 4 to 15 mm, more preferably a spacing between at least a
portion of the structural strands is in the range of 9 to 13
mm.
[0017] In one form, the invention provides a fin for surf craft
comprising: a fin body; and at least one layer of structural
strands, located within the fin body; wherein the structural
strands are in one or more woven arrangements that are at least one
of an open weave and a scrim; wherein the structural strands have a
physical property greater than a corresponding physical property of
other material forming the fin body; and wherein the physical
property is selected from at least one of a toughness, a tensile
strength, an elastic moduli and a Youngs modulus. Preferably,
further including a core structure located within the fin body.
Preferably at least one layer of structural strands in one or more
arrangements is embedded within a body of the fin such that the
layer of structural strands is substantially parallel to a face of
the core structure. Preferably at least one layer of structural
strands are located intermediate the core structure and at least
one of the opposing faces of the fin. Preferably the core is at
least one of a foam core structure and a solid, non-foam core
structure. Preferably at least a portion of the core structure is
made of at least one of PVC foam, polyurethane foam, resin
impregnated fibreglass, hardened resin, polyester mat,
microspheres, plastic, bamboo and wood.
[0018] Preferably further including at least one layer of
unidirectional carbon fibre fabric towards a base portion of the
fin body, more preferably at least one layer of carbon fibre fabric
is located about a periphery of the fin body.
[0019] Preferably a sweep angle of the fin is in the range of 20 to
60 degrees.
[0020] In yet another form, the invention provides a method of
controlling a fin physical property for a surf craft, the method
comprising: selecting one or more structural strands having a
structural strand physical property greater than a corresponding
physical property of other materials in a body of the fin;
selecting a number of structural strands to provide the fin
physical property; providing a layer of the structural strands in
one or more arrangements; and embedding the layer of structural
strands in the body of the fin; whereby varying at least one of the
structural strands selection, the number of structural strands or
the arrangement of the structural strands varies the fin physical
property; and wherein the fin physical property is selected from at
least one of: a stiffness characteristic, a bending resistance, a
twisting resistance, a resistance to a deflection, a flexibility
and a high elastic recoil; and wherein the structural strand
physical property is selected from at least one of: a toughness, a
tensile strength, an elastic moduli and a Youngs modulus.
Preferably the step of providing a layer of structural strands
includes the use of a template to locate one or more structural
strands of one or more arrangements. Preferably the step of using a
locating template further includes providing at least one of pins,
adherents and securing systems to locate one or more structural
strands. Preferably the step of using a locating template further
includes the steps of: providing one or more reliefs machined into
the template, and laying individual structural strands into
respective reliefs to form a three dimensional structural strand
layer. Preferably the step of providing a layer of structural
strands includes the use of a numerically or a computer controlled
machine to locate one or more structural strands of one or more
arrangements.
[0021] Preferably the step of providing a layer of structural
strands further includes a step of: configuring the arrangement of
structural strands in a layer to vary the fin physical property.
Preferably further including providing one or more structural
strands largely parallel to a sweep angle of the fin such that the
fin is provided with an increased resistance to a twisting of the
fin. Preferably further including providing one or more structural
strands at a first angle of up to 20 degrees to a sweep angle of
the fin to provide the fin with an increased resistance to a
twisting of the fin. Preferably further including providing one or
more structural strands at a second angle in the range of 20 to 40
degrees to the vertical axis of the fin such that the fin is
provided with an increased resistance to a deflection from the
vertical axis.
[0022] A fin for surf craft produced according to the methods
described above
[0023] In an alternate form, the invention provides a fin for surf
craft substantially as described herein and a method of controlling
a stiffness characteristic or other desired physical property of a
fin for a surf craft substantially as described herein.
[0024] Further forms of the invention are as set out in the
appended claims and as apparent from the description.
DISCLOSURE OF THE INVENTION
Brief Description of the Drawings
[0025] The description is made with reference to the accompanying
drawings; of which:
[0026] FIG. 1 is a perspective, representative view of a
surfboard
[0027] FIG. 2 is a side elevation view of a fin from the surfboard
of FIG. 1.
[0028] FIG. 3 is a bottom view of a fin of FIG. 2.
[0029] FIG. 4 is a "peel-away" or partially exploded perspective
view of a side fin in an embodiment of the present invention.
[0030] FIG. 5 is a side elevation view of the fin embodiment of
FIG. 4.
[0031] FIG. 6 is a plan view of a template board.
[0032] FIG. 7 is a schematic showing a layup of three arrangements
of a structural strands layer embodiment on the template board.
[0033] FIG. 8 is an enlarged view of the circled region in FIG.
7.
[0034] FIGS. 9 to 13 are respective side, plan, end and bottom
elevation views of a FEA analysis of homogeneous fin under an
applied force.
[0035] FIGS. 14 to 18 are the same elevation views of the fin of
FIGS. 9 to 13 with no force applied.
[0036] FIGS. 19 to 42 are to further embodiments of the invention
in side elevation views only, unless otherwise indicated.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0037] FIG. 1 is a perspective, representative view of a surfboard
110 to illustrate the main features associated with surfboards in
general. The surfboard 110 has a board 112 with a deck 114 that the
surfer stands on. The board 112 has a nose 116, a tail 118 and two
rails 120 defining the generally longitudinal edges of the board
112. To an underside 122 of the board 112 one or more fins 124, 126
are typically attached, usually towards the tail 118 but for high
performance surfboards and other surf craft the fins may be located
at a variety of locations along the underside of the board. The
surfboard 110 illustrated as an example has three fins 124, 126 in
a "thruster" configuration however surfboards may also have one,
two ("twin fin"), four or more fins in a variety of configurations.
An outside face 310 and inside face 312 of the side fin 124 are
described in detail below with respect to FIG. 3.
[0038] The overall general axes of orientation to a surfboard 110
may be a vertical axis 128, a transverse or "sideways" axis 130 and
a longitudinal or "stringer" axis 132.
[0039] FIG. 2 is a side elevation view of a fin 124, 126 to
additionally illustrate the main features associated with a fin.
The fin may have a base 210 with attachment features, tabs or
attachment means 212 which enable the fin 124, 126 to be suitably
attached or secured to the underside 122 of the board 112. It will
be readily appreciated that there may be a variety of attachment or
securing means for a fin to an underside of a board. The fin may
have a leading edge 214 that is towards the nose 116 of the board
112 and a trailing edge 216 which is towards the tail 118. A tip
218 of the fin may be also used to define a sweep angle 220 of the
fin, as shown with the dashed lines, with respect to the vertical
axis 128. For reference in the following detailed description a
rotation or twist 222 about the vertical axis 128 of the fin 124,
126 may occur in use. Alternatively a rotation or twist component/s
may occur about an axis corresponding to the dashed line in FIG. 2
corresponding to the sweep angle from the base 210 to the tip 218
of the fin. A vertical height or depth 224 dimension from the base
210 to the tip 218 of the fin may also be defined as shown in FIG.
2. The base 210 may have a base length 226 dimension as shown in
FIG. 2.
[0040] FIG. 3 is a bottom view of the fin in FIG. 2. The fin shown
is an example of a side fin 124 where an outside face 310 may be
more curved than an inside face 312 of the fin 124. The outside
face 310 of the fin 124 corresponds to the face closest to the rail
120 of the board 112 whilst the inner face 312 is the opposing face
to the outer face 310. The different respective curvatures of the
faces 310, 312 are configured to form an airfoil which induces a
sideways hydrodynamic force upon the side fin 124 and thereby
providing lift, as the fin travels through a wave and in particular
across the face of a wave.
[0041] The side fin/s 124 and/or centre fin/s 126 may also
experience a variety of other hydrodynamic forces upon them during
turns and complex manoeuvres which may cause them to deflect and/or
twist from their at rest positions.
[0042] FIG. 4 is a "peel-away" or partially exploded perspective
view of a side fin 410 in an embodiment of the present invention.
For reference FIG. 5 is a side elevation view of the fin 410 of
FIG. 4, viewing the outside face 310. In FIG. 4 a core 412 may
optionally be included to reduce the weight of the fin, provide
positive buoyancy in water and/or as further described below. The
core 412 may be a solid (non-foam) or a foam core, where a foam
core includes air pockets within that may be partially or fully
filled with impregnating resin. Solid cores may be made of resin
impregnated fibreglass, hardened resin, plastic, bamboo or wood.
Alternatively, foam cores may be PVC foam, polyurethane (PU) foam
or an advanced foam core materials such as Lantor Coremat as
described at www.lantor.nl. The Lantor Coremat being a nonwoven
polyester mat containing microspheres. Layers of fibreglass fabric
414 may optionally be present, the two layers illustrated in FIG. 4
being only illustrative. Many more layers of fibreglass fabric 414
may be present on either side of the core 412 depending on the
particular fin type and shape being designed/manufactured. An
optional outer layer of black polyester veil 416 for each face 310,
312 of the fin may be included to promote resin flow, as well as
improve the external finish and appearance of the fin 410. A
further, optional outer layer of uni-directional carbon fibre
fabric 418 may be included near the base 210 of the fin 410;
possibly extending to the attachment means 212 to improve stiffness
and strength at those parts of the fin body.
[0043] A description of the commonly available materials used to
manufacture fins as illustrated in FIG. 4 is provided in the
following by way of example only. The fibreglass fabric 414 may be
of 6 oz, close, plain weave or of other readily available
fibreglass reinforcing fabrics. The core may be a PVC foam of a 1.3
to 2.5 lb/cubic foot density PVC foam, black silk or polyester veil
and urn-directional carbon fibre fabric of 300 gsm (grams/metre
squared) weight. It will be readily appreciated that these commonly
available materials may be varied in terms of whether they are
included in a fin body and what may be selected for their use as
would be exercised by a person skilled in the art of surf craft,
surfboards in particular, design and manufacture.
[0044] The embodiment of the invention in FIG. 4 shows a structural
strand layer 420 that may include high tensile carbon fibre strands
422, 424 and high tensile strength and toughness Kevlar 426
strands. Structural strand examples are described in detail further
below. The layer of structural strands 420 features structural
strands which may have a tensile strength substantially greater
than the other materials typically used in a fin body. The use of a
discrete structural strand layer 420 provides an economic and ready
technique to vary and control a stiffness characteristic physical
property of the fin in a variety of directions or about a variety
of axes of rotation; without varying the other common components
that may be used in a fin body.
[0045] The term "stiffness characteristic" as a physical property
in the following detailed description and claims is taken to
include: [0046] The resistance of the fin to deflection or twist
forces in a variety of directions. Or in other words a twisting
resistance and/or a bending resistance. [0047] The flexibility of
the fin in a variety of directions or about a variety of axes.
[0048] High elastic recoil or restoration of the fin after a force
or a twist is applied to it is released. For example the snapping
back of the fin after it has been deflected due to forces applied
during a turn or complex manoeuvres. In other words energy or work
put into the fin in a turn is returned, with little or no loss, to
the surfer or rider of a surf craft at the completion of a turn.
[0049] Stiffness, resilience and/or flexibility physical properties
imparted to the fin by the combination of various materials of
various tensile strengths, elastic moduli and other properties into
the fin construction.
[0050] In addition toughness as a physical property in the
following detailed description and claims is taken to include a
comparatively moderate tensile strength material with improved
ductility, for example Kevlar/aramide fibres may have a higher
toughness compared with carbon fibres. Fibres with superior
toughness have a high degree or resistance to repeated twisting
and/or bending.
[0051] The carbon fibre strands 422 may be largely parallel to the
sweep 220 of the fin 410 or offset from the sweep angle by up to 20
degrees, preferably approximately 10 degrees in the example shown
in FIG. 4. The structural strands 422 may be introduced as a first
arrangement to control how much the fin resists twisting, in
particular about the vertical axis. Or in other terms how much
energy is retained or stored in the fin from its twisting in use.
The use of more structural strands in the first arrangement will
increase the resistance to twisting by the fin. The carbon fibre
strands 424 that are offset to the vertical by 20 to 40 degrees,
preferably approximately 30 degrees, may be introduced as a second
arrangement to modify how much the fin resists deflection from the
vertical axis. Preferably the direction of the offset to the
vertical for strands 424 is towards the fin leading edge 214. The
use of more structural strands in the second arrangement will
increase the resistance to deflection from the vertical axis for
the fin. As a general comment, the stiffness characteristic that
may be imparted by a structural strand, to a fin, being largely in
the longitudinal/length direction of the strand and proportional to
the number of structural strands and the structural strand physical
properties. The largely vertical Kevlar strands 426 may be
additionally introduced as a third arrangement to improve the
stiffness characteristic as well as the toughness and strength of
the fin so that it may resist breakage.
[0052] A description of the structural strands used in the
structural strand layer 420 is provided in the following by way of
example only. "3 k" (3,000 filaments per strand) unidirectional
carbon fibre strands in a largely ribbon form, "toe" form, may be
used. "3 k" unidirectional Kevlar or Aramide equivalents strands in
a substantially ribbon form may be used. Typically the ultimate
tensile strengths of carbon and Kevlar/Aramide fibres may be at
least 1.5 times or 2 times (2.times.) or more than commonly used
fibreglasses such as E-glass and more than the other commonly used
materials in a fin body. Similarly the elastic moduli such as
Youngs modulus for carbon fibre and Kevlar/Aramide equivalents may
be at least 1.5 times (1.5.times.), 2 times, 5 times or more than
commonly used fibreglasses such as E-glass and more than the other
commonly used materials in a fin body. The width of ribbon strands
may be in the approximate range of 0.5 to 3 mm or more preferably
in the range of 1 to 2 mm. The ribbon strands may have a thickness.
The thickness of a ribbon strand may be greater than 0.1 mm.
Natural fibres and synthetic fibres (in addition to those mentioned
already) may also be suitable with appropriate resin, plastic
and/or binder systems. It will be readily appreciated that these
structural strand materials may be readily varied in terms of what
may be selected for their use as would be exercised by a person
skilled in the art of surf craft, surfboards in particular, design
and manufacture. Furthermore the person skilled in the art would be
guided in their choice of structural strands by their superior
physical properties in comparison to the other materials used in
the construction of the fin; for example carbon fibre over
fibreglass and via a property such as tensile strength.
[0053] In one embodiment a layer of the structural strands may be
fabricated by use of an aluminium template 610 as shown in FIG. 6
in plan view. The template may have marked upon it the outline 612
of the fin 410, marker lines 614 for the location for the carbon
fibre strands 422 in the sweep direction or angle 220, marker lines
616 for the carbon fibre strands 424 that may be 30 degrees from
the vertical axis of the fin outline 612 and marker lines 618 for
the Kevlar strands 426.
[0054] FIG. 7 shows the layup of three arrangements of structural
strands 422, 424, 426 on the template board 610 to form a layer of
structural strands 420. A first parallel arrangement 710 of carbon
fibre strands 424 that are offset approximately 30 degrees to the
vertical axis of the fin outline 612 may be hand laid first. The
spacing between the parallel carbon fibre strands 424 may be chosen
to be in the range of 9 to 13 mm for a fin of approximate depth 224
of 100 mm. A second parallel arrangement 712 of Kevlar strands 426
may then be laid down. The spacing between the parallel Kevlar
strands 426 may be chosen to be in the range of 4 to 8 mm for a fin
of depth 224 of 100 mm. The Kevlar arrangement may then be followed
by a third parallel arrangement 714 of carbon fibre strands 422
that may be in the sweep angle 220 direction of the fin outline
612. The spacing between the parallel carbon fibre strands 422 may
be chosen to be in the range of 9 to 13 mm for a fin of depth 224
of 100 mm. It will be readily appreciated that the numerical values
for strand spacing and orientation are to obtaining a particular
stiffness characteristic and are only illustrative. For example a
fin of approximate depth of 111 mm may have a spacing between the
parallel carbon fibre strands 424 in the range of 9 to 15 mm or
more preferably in the range of 10 to 12 mm. Other examples are
given below with respect to FIGS. 19 to 42, where the relative,
proportional and/or angular relationships between the structural
strands are shown.
[0055] To aid in the laying up of the strands for each arrangement,
pins or other locating, fixing, securing or otherwise aid devices
(not shown) may be used at the periphery of the template 610 to
locate and/or secure the strands in a desired arrangement. More
complex arrangements or configurations may also be laid up and
these are described below in detail with respect to FIGS. 19 to 42.
For these more complex arrangements further locating/securing
systems such as pins, adherents and the like may be used to
facilitate the forming of more complex arrangements of the
structural strands.
[0056] In the course of laying up the arrangements 710, 712, 714 of
structural strands the individual strands may be impregnated with a
suitable resin or binder in order that overlapping structural
strands may be adhered together. FIG. 8 is an enlarged view of the
circled region in FIG. 7. FIG. 8 shows the resin or binder 810
adhering overlapping 812 structural strands 422, 424, 426 together.
The template board 610 may be pre-coated with a release agent to
prevent the adhering of the resin or binder 810 to the template
610.
[0057] In the above example of forming a structural strand layer
420 the layer is not woven, that is the structural strands are not
interlaced. In addition the layer is in the form of a scrim with
clear apertures 814. From the above examples of ribbon strand
widths and strand spacing the relative clear aperture may be from
approximately 1 to 30 times (1.times.-30.times.) one ribbon strand
width or more preferably from 4 to 13 times (4.times.-13.times.)
one ribbon strand width. In further embodiments of the structural
strand layer, described in detail below with respect to FIGS. 19 to
42, the structural strands from various arrangements may have some
or all of their strands interlaced in some fashion to form a woven
arrangement or scrim for the structural strand layer.
[0058] The technique for forming the structural strand layer may
also be adapted to a computer or numerically controlled apparatus
to manufacture the structural strand layer. A numerically
controlled (NC) machine (and/or computer controlled) may be
particularly suited for the arrangements/configurations described
below with respect to FIGS. 19 to 42. For example an embroidery
machine may be adapted to lay out the structural strand layer.
[0059] The scrim structural strand layer may then be die or
otherwise cut into the desired outline which for the example above
is the full outline 612 of the fin. The structural strand layer may
then be appropriately inserted into a mould of a fin with the other
fin components, for example described above with respect to FIG. 4.
In order to form the fin body a suitable resin system or plastic
together with possible additives such as fillers and/or colour
agents may then be injected into the mould to impregnate all the
reinforcing fabrics and the structural strand layer to form the fin
body. Resin Transfer Moulding (RTM) is one common example of a mass
production technique for forming the fin. Compression moulding may
also be used, by way of example.
[0060] Alternatively the scrim structural strand layer may be
directly removed from the template board 610 without cutting to the
fin outline 612. The scrim structural strand layer may then be
appropriately incorporated into a traditional fin panel of
fibreglass sheet and resin, formed by machine and/or hand. A
desired fin may then be machine cut (for example NC machine) from
the fin panel incorporating the structural strand layer. The
machine cut fin may then be hand finished and polished.
[0061] Without wishing to be bound by theory, Finite Element
Analysis (FEA) may be readily done for a typical homogeneous fin
(not incorporating a structural strand layer). FIGS. 9 to 13 show
the results of an FEA model of a homogeneous fin being subjected to
a force applied to the normal of face 312 of a side fin 124, 410.
The applied force simulates the sideways force that a side fin may
experience when: travelling across the face of a wave, in a
manoeuvre and/or when a fin is at a high angle of attack to the
bulk fluid flow stream under the surfboard. FIG. 9 is a side view,
FIG. 10 is a plan view, FIG. 11 is an end view, FIG. 12 is a bottom
view and FIG. 13 is a front view. Contour lines 910 to 918 have
been placed on each of the views to show the amount of horizontal
displacement of the fin, from its rest position, by an applied
force. Contour line 910 is approximately 20 mm at the tip 218,
contour line 912 is approximately 13 mm, contour line 914 is
approximately 10 mm, contour line 916 is approximately 3 mm and
contour line 918 at the secured base 210 is 0 mm. For comparison
purposes FIGS. 14 to 18 are views of the same fin with no force
applied. FIG. 14 is a side view, FIG. 15 is a plan view, FIG. 16 is
an end view, FIG. 17 is a bottom view and FIG. 18 is a front
view.
[0062] It is apparent from FIGS. 9 to 18 that a side fin travelling
along the face of a wave, or otherwise as per above, may bend
sideways in the direction of the transverse axis 130 as well as
twisting/rotating about the vertical axis 128. Altering the
stiffness characteristic of such a fin by incorporating a
structural strand layer may readily affect the response of the fin
to applied forces in a number of directions.
[0063] The technique described above for producing a structural
strand layer allows for arrangements or configuration of the
structural strands within the structural strand layer which may be
very difficult or impossible to attain with commercially available
stock reinforcing fabrics. In the following figures of FIGS. 19 to
42 further embodiments of the invention are illustrated in side
elevation views only. FIGS. 19 to 42 primarily illustrate the layup
of the structural strands; the other common components of a fin
have been omitted for clarity. In addition in FIGS. 19 to 42 the
Kevlar strands have been omitted for clarity as well as indicating
that they may be considered optional.
[0064] In a number of the FIGS. 19 to 42 a core 412 may be shown,
but as for the embodiments disclosed above: the core 412 is an
optional component. However in some instances in the below the core
may also serve as a useful locational reference where the
embodiment may have two structural strand layers or arrangements of
a structural stand layer continue over two layers about the core.
An example of a structural strand for the embodiments of FIGS. 19
to 42 may be carbon fibre strands.
[0065] FIGS. 19 and 20 are the opposing side elevation views of a
fin 1910 featuring a structural strand layer with two arrangements.
The first arrangement 1912 has radial structural strands 1912 with
a common origin 1914 at the intersection of the base 210 and
leading edge 214 of the fin 1910. Or in other words, the structural
strands may extend from one common point to form a radial pattern
or formation. The second arrangement 1916 has arc strands 1912 with
a common arc centre being also the origin 1914. In this structural
strand layer the first and second arrangements may be laid up
either in a non-woven or woven (interlaced) manner to form a scrim.
However in comparison to commercially available reinforcing fabrics
there are no substantially unidirectional structural strands or
structural strands that are orthogonal to each other over their
full length of use within the structural strand layer.
[0066] FIGS. 21 and 22 are again opposing side elevation views of a
fin 2110. The first arrangement 2112 also has radial structural
strands 2112 but with a virtual origin (not shown) below the base
210. The second arrangement 2114 is also radial structural strands
but with a different virtual origin (not shown) which is below the
base 210 but forward of the leading edge 214.
[0067] FIGS. 23A and 23B are again opposing side elevation views of
a fin 2310. However this structural strand layer features two
arrangements of partially continuous radial strands. The first
arrangement 2312 of radial strands originates from a virtual origin
(not shown) to the rear of the trailing edge 216. The radial
strands 2312 radiate to the base 210 and leading edge 214. At the
leading edge 214 a portion of the radial strands 2312 are
re-directed (or "reflected") from the leading edge 214 to form a
second arrangement of continuing radial strands 2314 that continue
to the base 210. This structural strand layer embodiment may have
the effect of providing additional structural strands and
consequently stiffness to the base 210 of the fin 2310 in
comparison to the portion of the fin 2310 towards the tip 218.
[0068] FIGS. 24 to 26 illustrate two related fin embodiments 2410,
2510 where both structural strand layers originate from the leading
edge 214. The first arrangement of structural strands 2412, 2512
radiates to the tip portion 218 of the fins 2410, 2510. The second
arrangement 2414, 2514 radiates to the base 210 and lower portion
of the trailing edge 216. However the second embodiment 2510
employs the use of a core 412 to separate a first arrangement 2512
from a second arrangement 2514.
[0069] FIGS. 27 and 28 are a related embodiment to FIG. 5, however
the structural strand layer for fin 2710 has only one arrangement
2712 of structural strands and the strand arrangement is slightly
radiused with a substantial portion of the structural strands being
in the general direction of the sweep 220 of the fin 2710. The fin
2710 also features a portion of uni-directional carbon fibre fabric
418 as described for FIGS. 4 and 5.
[0070] FIGS. 29 and 30 are to a fin 2910 embodiment where the
structural strand layer may have two arrangements of structural
strands with the individual strands being continuous through both
arrangements. The first arrangement 2912 of largely parallel
structural strands projects in a generally vertical direction from
the base 210 and then executes a fold over 2916 or strand
re-direction as produced on the template 610 or the like. The
re-direction 2916 of the structural strands may be such that the
structural strands again continue in a parallel fashion for the
second arrangement 2914 directly to the mid section of the trailing
edge 216. However the second arrangement 2914 features
substantially closer adjacent structural strands than for the first
arrangement 2912. Such a reinforcing layup may not be achievable
with commercial reinforcing fabrics.
[0071] The stiffness characteristic of the fin 2910 in the region
of the second arrangement 2914 may be higher than that of the
region of the first arrangement 2912 due to the combined effect of
the reduced spacing between adjacent structural strands together
with the overlap between the second 2914 and first 2912
arrangements. Accordingly the fin 2910 may have stiffness
characteristic of being very stiff towards the base and in
particular for a portion to the mid section of the trailing edge
216 but with a particularly flexible or whip-like tip 218. FIG. 30
shows the presence of a mirror structural stand layer 2912'',
2914'' to FIG. 29, which may further promote the stiffness
characteristic described.
[0072] FIGS. 31 and 32 illustrate a fin 3110 embodiment with a
structural strand layer with a first arrangement 3112 and a second
arrangement 3114 to also vary the stiffness characteristic in
different portions or regions of the fin 3110. The first
arrangement 3112 of parallel structural strands may feature a first
narrow spacing 3116 and second larger spacing 3118 between adjacent
structural strands. The first arrangement 3112 projects from a tip
portion 218 towards the base 210 along the general sweep angle 220
direction. At a re-direction band 3120 the structural strands may
be redirected approximately orthogonally as shown. The redirection
3120 may be such that in the second arrangement 3114 spacing
between adjacent structural strands is uniform. This structural
strand layer for fin 3110 may achieve a greater stiffness
characteristic for the base portion of the fine 3110 compared with
the rest of the fin body. This fin 3110 embodiment may have an
advantage to that described with respect to FIGS. 4 and 5 in that
the urn-directional reinforcing fabric 418 may not be
necessary.
[0073] FIGS. 33 and 34 are to a fin 3310 embodiment similar to that
of FIGS. 29 and 30; where the structural strand layer may have two
arrangements of structural strands with the individual strands
being continuous through both arrangements. However the first
arrangement 3312 from the leading edge 214 portion of the base
extends generally towards the tip 218. At a re-direction or
fold-over band 3316 the first arrangement 3312 is twisted through
180 degrees to form the second arrangement 3314 which continues to
the tip 218 as shown.
[0074] FIGS. 35 and 34 are to a fin embodiment 3510 with four
arrangements of structural strands. The first 3512 and second 3514
arrangements may be a zigzagged arrangement from one edge of the
fin to another edge to approximately the mid portion of the fin
3510 as shown in FIG. 35. The first 3512 and second 3514
arrangements may be overlayed or interlaced. In FIG. 36 the third
3612 and fourth 3614 arrangements are also shown in a zigzagged
fashion, but extending from the mid-portion of the fin 3510 to the
tip 218.
[0075] FIG. 37 is a fin embodiment 3710 where the first arrangement
3712 zigzags up the leading edge 214 with one side of the first
arrangement interlaced/woven into the second arrangement 3714 which
zigzags up the trailing edge 216, from base 210 to tip 218.
[0076] FIG. 38 is to a fin embodiment 3810 that is an alternate
embodiment to that of FIG. 37. In FIG. 38 the structural strand
layer 3812 features lighter gauge structural strands 3814, 3816 but
in a higher density/pitch in the weaving/interlacing. This fin 3810
embodiment of the structural strand layer may have an increased
stiffness to the leading edge 214 but allows the rest of the fin
3810 to twist and flex.
[0077] FIGS. 39 and 40 are to a fin embodiment 4010 where a three
dimensional structural strand layer 3912 may be formed by the use
of a template block 3910 with a relief machined 3914 into it. The
structural strand layer 3912 may have the individual structural
strands 3916 laid up into the relief 3914. Once all the strands
3916 have been placed a layer of resin may then be applied to form
the three dimensional structural strand layer 3912 as a shell. The
three dimensional structural stand layer 3912 may then be
incorporated into a fin body as described previously; however
because of the relief of this structural strand layer 3912, it may
be positioned close to the surface of the fin face 310. One or more
layers of fibreglass fabric may be located between the fin face 310
surface and the three dimensional structural strand layer 3912.
[0078] FIGS. 41 and 42 are to another fin embodiment 4110
incorporating a number of elements from the prior embodiments
described above. In this embodiment 4110 the primary arrangement
4112 of structural strands generally originates from the base 210
of the fin and may then be directed to the fin leading edge 214.
The primary arrangement may then be folded over or re-directed at
the fin leading edge 214 to then continue as the secondary
arrangement 4114 of structural strands proceeding generally to the
fin trailing edge 216 as shown. It will be readily appreciated that
the folding over or redirecting from the first to the secondary
arrangement may be achieved using the lay-up template 610 described
above with respect to FIGS. 6 and 7. For example the fold over or
redirection may be slightly offsetted to the fin leading edge as
allowed for by use of the lay-up template 610. Alternatively the
lay-up may be with two different carbon strands for each
arrangement, the intersection of the strands for the primary and
secondary arrangement being along all or part of the leading edge
of the fin.
[0079] The spacings between the structural strands of the primary
and secondary arrangements 4112, 4114 vary from the base 210 to the
tip 218 so as to provide an increased stiffness characteristic
towards the base 210 of the fin. A reduced spacing of the
structural strands towards the base consequently increases the
stiffness characteristic as well as providing a gradient of the
stiffness characteristic across the depth of the fin.
[0080] The carbon fibre strands of the secondary arrangement 4114
may be largely perpendicular to the sweep angle of the fin as shown
in FIGS. 41 and 42. Whilst the carbon fibre strands of the primary
arrangement 4112 may be offset to the secondary arrangement 4114 by
an angle in the range of 20 to 40 degrees or preferably
approximately 30 degrees.
[0081] The primary and secondary arrangements 4112, 4114 of
structural strands may be analogous to the embodiments of FIGS.
23A, 31 and 35, for example. The closer spacing of the structural
strands towards the fin base 210 may be analogous to FIGS. 23A and
31 for example.
[0082] In FIGS. 41 and 42 a core 412 is shown which for this
embodiment may be of Lantor Coremat as previously described or any
other suitable material. In FIGS. 41 and 42 the core 412 is shown
on one side of the two arrangements 4112, 4114, however as
described in detail below the structural strand arrangements or
scrims may be on both sides of the core 412 as may be used for the
centre fin of a thruster configuration, FIG. 1, whilst the single
sided structural strand arrangement of FIGS. 41 and 42 may be for a
side fin of a thruster configuration. In an alternate embodiment
for a centre fin a scrim/structural strand arrangement may be
sandwiched between two cores such that the centre fin has the
appearance of FIG. 42 from both sides.
[0083] Optionally, another arrangement of largely horizontal,
parallel fibreglass strands 4116 may be further included in the fin
construction. Alternatively the tertiary arrangement 4116 may use
structural strands of Kevlar or aramide equivalents instead of
fibreglass in order to improve the toughness performance of the fin
as well as its stiffness characteristic. The fin embodiment 4110
may be constructed using RTM injection with vinyl ester as
described above.
[0084] The embodiments of FIGS. 19 to 42 are also examples of how
the spacing and gauge of the structural strands may differ between
different structural strand layers and between different strand
arrangements within a structural strand layer.
[0085] It will be readily appreciated that elements from the
described embodiments may be used to formulate other embodiments of
the invention and still be within the scope of the invention.
[0086] In addition, between side fin/s 124 and centre fin/s 126 of
surfboards the number and type of structural strand layers may
differ. A greater stiffness characteristic for the centre fin 124
compared with the side fins 126 may be obtained by the use of a
structural strand layer imparting a greater stiffness
characteristic and/or multiple structural strand layers. For
example: to the multiple structural strand layers for a centre fin,
two structural strand layers may be used, one on each side of the
core 412. In addition the choice of a core material and the
dimensions of the core may also be varied in order to further
change the stiffness characteristic or toughness of a fin. It will
be readily appreciated that greater stiffness for a fin may be also
achieved by changing the fin geometry/shape but this would also
impact upon the hydrodynamic drag and other hydrodynamic
properties.
[0087] The above described method and product of using a discrete
structural strand layer allows the stiffness characteristics in
terms of the amount of stiffness and distribution of the stiffness
to be readily varied across the face of the fin and thru the fin
body. For example to produce a component of twist about the
horizontal/longitudinal axis of a fin. In addition the deflection
and twist characteristics of stiffness may be varied from one face
to the other face of a fin by either the layup of strands within an
arrangement of a discrete structural strand layer and/or the
position of the structural strand layer within construction of the
fin. Fins with customised, multi-axis deflection and twist
characteristics may be readily produced and tested. The technique
disclosed here may be suitable for both small experimental and
custom-built production runs common in surf craft fin research and
development work and custom-built professional competition supply
as well as readily adaptable to mass production of a fin product
range with particular stiffness or flexibility characteristics.
[0088] For surfboards a fin product range incorporating a
structural strand layer may be, for example, to: [0089] A surf
board rider's proficiency, strength and style of surfing. For
example experienced surfers may prefer a stiffer fin range to
improve surfboard performance. Professional surfers may require a
custom-built fin with a stiffness characteristic tailored to their
particular requirements. [0090] A surfboard rider's weight: heavier
surfers may require stiffer fins to maintain hold through turns.
The term "hold" is often used to describe the level of slippage
movement of the tail of the surfboard during turns, particularly
aggressive turns.
[0091] An example fin product range for surfboards may have the
approximate dimensions and angles of: [0092] "Large", a
depth/height 224 dimension of 119 mm, a base length 226 dimension
of 118 mm and a sweep angle 220 of 34 degrees. [0093] "Medium", a
depth/height 224 dimension of 113 mm, a base length 226 dimension
of 111 mm and a sweep angle 220 of 34 degrees. [0094] "Small", a
depth/height 224 dimension of 110 mm, a base length 226 dimension
of 105 mm or 109 mm and a sweep angle 220 of 34 degrees. [0095]
"Custom-Built/Competition", a depth/height 224 dimension of 119 mm,
a base length 226 dimension of 114 mm and a sweep angle 220 of 36
degrees. [0096] Sweep angles for surfboard fins according to the
invention may be in the range of 20 to 60 degrees or more
preferably in the range 26 to 56 degrees or in another preferred
embodiment approximately 33 degrees.
[0097] A broad, simple example of a stiffness characteristic
specification for a fin product range may be the amount of
horizontal displacement of the fin tip 218 to an applied force as
described above with respect to FIGS. 9 to 18. By way of example
fins with various structural strand layers may provide a range in
horizontal displacements from 5 to 25 mm or 10 to 20 mm of the tip
218 for applied forces typical in variety of surfboard uses.
[0098] Without wishing to be bound by theory we believe that the
ability to readily vary the stiffness characteristic across a fin
may enable further improvements in the performance of a surfboard
in the areas of: [0099] Stall characteristics [0100] The hold of
the fin/s during a turn and complex manoeuvres. [0101] The
sensation of "drive"/acceleration into and out of a turn. Stiffer
fins tend produce a greater sensation of drive. [0102] The
responsiveness of a surfboard may be affected by the stiffness of
the fin/s. Stiffer fins may result in a more responsive surfboard.
A more forgiving surfboard may result from more flexible fin/s.
[0103] When transitioning from one turn to another a stiff fin with
a high degree of elastic recoil may provide increased speed and
acceleration from one turn to another as the surfboard transitions
from one side fin to the opposing side fin. [0104] Flex: To make a
fin that performs more efficiently the inventors had to ensure it
could flex in multiple directions. This invention's technology is
the latest development in fin flexion which draws on the material
lay-up of the fin, the cambered foil, and the overall fin template.
The result is a multi-directional flex pattern. This unique flex
pattern allows the fin to `load-up` and flex under pressure, and
then de-coil once the pressure is released. Ultimately the fin
stores energy during the transition between turns and then gives it
back to the surfer in the form of superior speed and acceleration.
The feeling can be compared to a slingshot, or whipping effect as
the surfer enters and then exits through the turning arc. [0105]
Foil: A highly efficient foil in combination with the invention can
be the defining element that makes for exceptional fin performance.
The highly cambered foil in the base of the fin provides drive and
hold, the low cambered foil in the tip provides stability and
allows the fin to release with control, even when the fin is pushed
to the limits. This cambered foil also increases the fin's stall
angle which helps to produce down-the-line speed and maintain
projection through the entire turning arc. [0106] Template: The fin
with the invention may feature an efficient, low aspect ratio
elliptical template. The long base increases drive, moderate volume
in the tip enhances the flex and coil characteristics, and the
smooth transitional trailing edge reduces water separation, which
is traditionally linked to cavitation. Translated, this means
increased speed and drive through minimal water disturbance. [0107]
Construction: Visually it's easy to see how technology and
performance overlap. Structurally, the fin may draw on a
combination of engineered Bi-axial Carbon (via two arrangements of
uni-directional Carbon) and Uni-directional Kevlar to achieve the
invention's flex pattern. The Uni-directional carbon fibre fabric
(418) base further increases stiffness in the base of the fin, and
helps to distribute pressure away from the plugs (of the surfboard)
by reducing the twisting forces on the fin tabs securing the fin to
the board. The Resin Transfer Moulding (RTM) process delivers
consistency across manufacturing and guarantees the integrity of
the flex and foils. Epoxy resin may be used to provide strength and
material stability, while a lightweight moulded core further
reduces the overall weight of the fin.
[0108] It will be readily appreciated that the above described
method for readily altering the stiffness or flexibility properties
of a fin of a surfboard may be readily applied to other surf craft
such as windsurfers, paddleboards, wave and surf skis,
kite-boarding, wake boards, and the like.
[0109] Although the invention has been herein shown and described
in what is conceived to be the most practical and preferred
embodiments, it is recognized that departures can be made within
the scope of the invention, which are not to be limited to the
details described herein but are to be accorded the full scope of
the appended claims so as to embrace any and all equivalent
assemblies, devices and apparatus.
[0110] In this specification, the word "comprising" is to be
understood in its "open" sense, that is, in the sense of
"including", and thus not limited to its "closed" sense, that is
the sense of "consisting only of". A corresponding meaning is to be
attributed to the corresponding words "comprise, comprised and
comprises" where they appear.
[0111] It will further be understood that any reference herein to
known prior art does not, unless the contrary indication appears,
constitute an admission that such prior art is commonly known by
those skilled in the art to which the invention relates.
* * * * *
References