Note: Descriptions are shown in the official language in which they were submitted.
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HYDROFOIL BOAT STABILIZER
BACKGROUND
[0001] The present invention relates to a hydrofoil boat stabilizer having a
true lifting
airfoilthydrofoil shape incorporated into the design, which provides lift to
the stern of the boat.
The hydrofoil boat stabilizer is attachable to a cavitation plate on the lower
drive unit of a boat
motor.
[0002] The skilled artisan understands that the drive system of a boat
generates the forward
thrust. The same skilled artisan also understands that the boat and drive
system are fighting the
forces of drag upon the boat as it rides low in the water. Thus, the higher in
the water, or "on the
plane," a boat rides, the less drag it encounters. Therefore, it is desirable
to reduce the amount of
boat drag.
[0003] Boats inherently have drag from many sources, and one way to reduce
drag is to get
the boat on the plane faster by providing lift to the lower drive unit with a
boat stabilizer.
Unfortunately, while providing lift and reducing drag on the boat, these same
stabilizers also
introduce additional drag, limiting the overall performance of the boat and
motor.
[0004] In their attempt to manage water flow, the designers of the known boat
stabilizers
inadvertently introduce one or more points of cavitation in and around the
stabilizer by choosing
a design that is not a true hydrofoil shape, or by choosing the wrong true
hydrofoil shape for the
application. As the speed of the boat varies, the position of the cavitating
water changes location
on the stabilizer and often increases in magnitude. Cavitation is the rapid
formation and collapse
of vapor pockets in moving water in regions of very low pressure. Accordingly,
cavitation is
controlled on the hydrofoil by keeping the maximum velocity that occurs on the
hydrofoil below
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the limit at which cavitation occurs, or has significant effect. This
cavitation of the water
introduces significant levels of drag.
[0005] It is desirable to have the "right" true hydrofoil shape for a boat
stabilizer. A true
hydrofoil shape is a hydrofoil designed and tested by using
aerodynamic/hydrodynamic design
principles and procedures, such as the foil design software, XFOIL Subsonic
Airfoil
Development System, from the Massachusetts Institute of Technology, or a
similar such
program. A true hydrofoil shape improves performance, and reduces both
cavitation and drag.
Various hydrofoil designers have produced and tested several true hydrofoil
shapes, each having
different performance characteristics across a wide range of performance
parameters at differing
speeds, to include lift, drag, profile drag, cavitation, and laminar-to-
turbulent transition. Some
non-limiting examples of hydrofoil shapes include the NACA 63-209, Eppler
E817, Eppler
E818, Eppler E836, Eppler 837, Eppler E838, Eppler E874, Eppler E904, Eppler
E908, and the
Speers H105. The "right" true hydrofoil shape is one that is applicable for
the particular
performance characteristics desired for the boat, engine and boat stabilizer.
For example, a
performance characteristic might be a constant, total laminar flow across the
entire hydrofoil
wing section for a given speed range.
[0006] Hydrofoil lift characteristics are balanced against drag and cavitation
resistance for
given speeds. Preferably, the hydrofoil will control cavitation across a broad
range of
speeds/velocities. One example of hydrofoil performance is the H105 hydrofoil
shape, which
has a profile drag that is nearly constant as the laminar-to-turbulent
transition point moves
forward on the upper surface of the hydrofoil. Simultaneously, the laminar-to-
turbulent
transition point moves aft on the lower surface as flow speed increases. This
results in the
example H105 hydrofoil maintaining nearly the same total amount of laminar
flow across it,
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thereby providing strong lift characteristics. By maintaining a constant
laminar flow, the rapid
formation and collapse of vapor pockets along the hydrofoil are reduced to a
constant level,
thereby reducing the opportunity for creation of additional drag due to
cavitation.
[0007] A need exists for a boat stabilizer that has a true hydrofoil shape,
low-drag and
minimizes cavitation on and around it. Additionally, a need exists for a
hydrofoil boat stabilizer
that provides good lift characteristics to minimize drag and cavitation.
SUMMARY
[0008] In accordance with the present invention, a hydrofoil boat stabilizer
is provided which
overcomes the deficiencies described above and has other advantages as well.
[0009] In one embodiment, the current invention provides a slip-on hydrofoil.
The slip-on
hydrofoil comprises a yoke and a pair of wings. The yoke includes a center
body defining a
longitudinal channel therein. The longitudinal channel has a first and second
side, and is open to
the front of the center body. The yoke also includes a pair of open-ended
slots oppositely
disposed in each of the channel sides, and extending along a substantial
length of the sides. The
open-ended slots are capable of receiving a cavitation plate of a boat motor.
The yoke includes a
tail section that is integrally formed with the center body. The tail section
covers a portion of the
longitudinal channel. The yoke includes a contoured trailing edge defined by
the tail section.
The contoured trailing edge angles upwardly. The pair of wings are integrally
joined with the
yoke and project outwardly therefrom. Each of the wings has a leading edge and
a trailing edge.
The trailing edges of the wings are seamlessly integrated with the contoured
trailing edge of the
tail section. There is a plurality of securing devices disposed through the
center body securing
the slip-on hydrofoil to a cavitation plate.
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[0010] In another embodiment, the current invention provides a hydrofoil. The
hydrofoil
comprises a yoke and a pair of wings. The yoke has a center body. There is a
longitudinal
channel defined by the center body. The longitudinal channel has oppositely
positioned walls
defining oppositely positioned slots therein. Each of the wings has a wing
tip, a root, and a
trailing edge. Each of the wings has a cross-sectional configuration of at
least one true hydrofoil
from the wing tip to the root. The pair of wings are joined to the yoke at the
root. There is at
least one non-invasive securing device for retaining said hydrofoil on a
cavitation plate.
[0011] In yet another embodiment, the current invention provides a minimum
cavitation,
low-drag hydrofoil. The minimum cavitation, low-drag hydrofoil comprises a
yoke and a pair of
wings. The yoke includes a longitudinal channel and a tail section. The
longitudinal channel has
a pair of oppositely positioned slots disposed in oppositely positioned walls.
The tail section
integrally covers a portion of the longitudinal channel. Each of the wings has
a wing tip, a root,
and a trailing edge. Each of the wings has a cross-sectional configuration of
at least one true
hydrofoil from the wing tip to the root. Each wing has at least one angle of
attack. The pair of
wings are joined to the yoke at the root. There is a contoured trailing edge
extending from the
tail section and seamlessly integrated with the trailing edge of the wings.
The contoured trailing
edge on the tail section is a juncture of a contoured flow surface area and an
upward sloping
bottom. There is a drag reducing surface on the hydrofoil. There is at least
one securing device
for retaining said hydrofoil on a cavitation plate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a front top perspective view.
[0013] FIG. 2 is a front bottom perspective view.
[0014] FIG. 3 is a back bottom perspective view.
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[0015] FIG. 4 is a plan view.
[0016] FIG. 5 is bottom view.
[0017] FIG. 6 is a side landscape view.
[0018] FIG. 7 is a front landscape view.
[0019] FIG. 8 is a back landscape view
[0020] FIG. 9 is a section view taken along lines 9-9 of FIG. 4.
[0021] FIG. 10 is a section view taken along lines 10-10 of FIG. 7.
[0022] FIG. 11 is a section view taken along lines 11-11 of FIG. 7.
[0023] FIG. 12 is a section view taken along lines 12-12 of FIG. 7.
[0024] FIG. 13 is a schematic of a representative example of a true hydrofoil
shape.
[0025] FIG. 14 is a side view of a hydrofoil positioned to slip onto the lower
drive unit of a
boat motor.
[0026] FIGS. 15A-D are schematic views of an additional connective device on
the
hydrofoil.
DETAILED DESCRIPTION
[0027] Referring to FIGS. 1-14, the hydrofoil apparatus is illustrated and
generally
designated by the numeral 10. Hydrofoil 10 is designed as a slip-on hydrofoil
having minimum
cavitation with low-drag characteristics. Hydrofoil 10 will slip onto
cavitation plate 12 of lower
drive unit 14 of a boat motor (not shown). Hydrofoil 10 is the combination of
yoke 16 and wings
18. Yoke 16 is designed to fit around cavitation plate 12 and lower drive unit
14 of a boat motor.
[0028] Regarding FIGS. 1-3, 5 and 9, yoke 16 includes center body 20,
longitudinal channel
22, and tail section 24. Yoke 16 also includes front 26, aft 28, sides 30, top
32 and bottom 34 of
center body 20. Front 26, aft 28 and sides 30 all have rounded edges
transitioning to bottom 34.
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Additionally, front 26 and aft 28 are sloped towards sides 30, thereby
reducing drag around yoke
16.
[0029] Yoke 16 centrally defines longitudinal channel 22 within center body
20.
Longitudinal channel 22 opens to front 26 and aft 28. Longitudinal channel 22
has channel first
side 36 and channel second side 38, which are oppositely positioned walls.
Open-ended slots 40
and 42 are disposed in channel first and second sides 36 and 38, respectively.
Open-ended slots
40 and 42 are oppositely positioned from each other. As illustrated, open-
ended slots 40 and 42
are approximately centered on channel sides 36 and 38. However, open-ended
slots 40 and 42
may be positioned above or below the depicted location by as much as about 25
percent without
significant degradation to hydrofoil 10 performance. Open-ended slots 40 and
42 are sized to
slip on cavitation plate 12 and around torque tab 44 affixed thereto.
[0030] Referring to FIGS. 2, 3, 9 and 14, open-ended slots 40 and 42 are
capable of receiving
cavitation plate 12. As illustrated, open-ended slots 40 and 42 extend along a
substantial length
of channel first and second sides 36 and 38, terminating near aft 28 of center
body 20 at slot wall
46. Slot wall 46 provides a receiving block for cavitation plate 12 that
prevents cavitation plate
12 from moving aftwardly in open-ended slots 40 and 42 once hydrofoil 10 is
slipped thereon.
Although not illustrated, yoke 16 and longitudinal channel 22 are optionally
adjustable to
facilitate placement of hydrofoil 10 on different boat motors and cavitation
plates 12.
[0031] Extending from yoke 16 onto contoured flow surface area 48 of tail
section 24 of
hydrofoil 10 is yoke drag relief 50. Yoke drag relief 50 is wedge-like in its
shape. Yoke drag
relief 50 eliminates hydraulic impingement on hydrofoil 10 at the point where
the water flow
departs from cavitation plate 12 and lower drive unit 14 of a boat motor.
Thus, yoke drag relief
50 reduces the drag acting upon hydrofoil 10.
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[0032] Referring to FIGS. 1-6, tail section 24 is integrally formed with yoke
16 across top 32
and center body 20 towards aft 28. Tail section 24 provides the connective
support structure for
yoke 16. A portion of tail section 24 covers longitudinal channel 22. Tail
section 24 terminates
beyond aft 28 of yoke 16 at contoured trailing edge 52.
[0033] The portion of longitudinal channel 22 covered by tail section 24 is
preferably about
one-half of the total length of yoke 16 and tail section 24 combined, or less.
As illustrated in
FIGS. 1-6 and 9, a small portion of longitudinal channel 22 and open-ended
slots 40 and 42 are.
covered by tail section 24.
[0034] Tail section 24 includes yoke drag relief 50. Yoke drag relief 50
provides for
transition of fluid, such as water, from cavitation plate 12 and lower drive
unit 14 of a boat motor
over transition flow edge 54, and onto and along contoured flow surface area
48 and spine 56.
Transition flow edge 54 is the transition point from yoke drag relief 50 and
contoured flow
surface area 48 and spine 56. Contoured flow surface area 48 and spine 56
provide water flow
onto and over contoured trailing edge 52. Both contoured flow surface area 48
and spine 56
terminate at contoured trailing edge 52.
[0035] Extending from bottom 34 at aft 28 is upward sloping bottom 58 of tail
section 24.
Contoured flow surface area 48 and upward sloping bottom 58 join together to
form contoured
trailing edge 52. Contoured trailing edge 52 is the juncture of contoured flow
surface area 48
and upward sloping bottom 58. As illustrated in FIGS. 1, 4, 6 and 9, contoured
flow surface area
48 provides an upwardly angling flow direction as it approaches contoured
trailing edge 52.
Similarly, upward sloping bottom 58 provides an upwardly angling flow
direction as it
approaches contoured trailing edge 52. Upward sloping bottom 58 has a steeper
upward slope
than that of contoured flow surface area 48. The resulting flow of water, as
it departs contoured
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trailing edge 52, has an overall reduction of turbulence, which in turn
reduces the cavitation and
drag imparted to hydrofoil 10.
[0036] As illustrated in FIGS. 1-8, wings 18 have leading edge 60, trailing
edge 62, wing tip
64 and root 66. Wings are seamlessly and integrally joined with yoke 16 at
root 66. In
particular, wings are integrally joined with center body 20 at root 66 and
form upper flow
channel 68 where upper surface of wings 18 join top 32 of yoke 16. Upper flow
channel 68
channels water in the transition zone between wing root 66 and yoke 16 towards
aft 28 and tail
section 24. To minimize drag from the separation of the water from trailing
edge 62 and
contoured trailing edge 52, trailing edge 62 and contoured trailing edge 52
are seamlessly
integrated together. The seamless integration of trailing edge 62 and
contoured trailing edge 52
provides for a low-drag release of the water from the hydrofoil tail section.
[0037] As illustrated in FIGS. 7, 10-12 and 13, wings 18 have cross-sectional
shape 70 that is
the configuration of a true hydrofoil. The configuration of a true hydrofoil
is illustrated in FIG.
13. Non-limiting examples of true hydrofoils include hydrofoils having the
designation of
NACA 63-209, Eppler E817, Eppler E818, Eppler E836, Eppler 837, Eppler E838,
Eppler E874,
Eppler E904, Eppler E908, and Speers H105. Some of the decision parameters
used to select the
true hydrofoil are based upon the speed, lift, and drag characteristics for
which the hydrofoil will
be utilized. In one preferred embodiment, the Speers H105 hydrofoil shape
satisfies all of the
desired characteristics of lift and drag for the different speeds hydrofoil 10
is to operate.
[0038] Preferably, wings 18 continuously retain the cross-sectional
configuration of the true
hydrofoil from wing tip 64 through root 66, including a plurality of angles of
attack, but at least
one angle of attack. Alternatively, the true hydrofoil shape transitions from
a first true hydrofoil
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shape to at least one other true hydrofoil shape for each angle of attack
based upon the broad
spectrum of performance parameters desired for hydrofoil 10.
[0039] As representatively illustrated in FIGS. 7 and 10-12, wings 18 have at
least three
angles of attack: first angle of attack 72, second angle of attack 74 and
third angle of attack 76.
FIG. 10 illustrates cross-sectional shape 70 from a section of wing 18 taken
near wing tip 64
having first angle of attack 72. FIG. 11 illustrates cross-sectional shape 70
from a section of
wing 18 taken along second angle of attack 74. In addition, FIG. 12
illustrates cross-sectional
shape 70 from a section of wing 18 taken along third angle of attack 76. FIGS.
10-12 include the
reference coordinates in order to illustrate the angle of attack.
[0040] Wings 18 in the configuration of a true hydrofoil provide for at least
one lifting
segment 78 having at least one angle of attack. Preferably, wings 18 have a
plurality of lifting
segments 78, whereby each lifting segment 78 has an angle of attack that is
separate from the
angle of attack of the lifting segment 78 immediately proximate thereto. Thus,
wings 18
preferably have a plurality of angles of attack.
[0041] The embodiment in FIGS. 7 and 10-12, representatively illustrates that
wings 18 have
at least angles of attack 72, 74 and 76, thereby providing low-to-medium-to-
high speed lift
characteristics. Having first, second and third angles of attack 72, 74 and 76
allows hydrofoil 10
to provide a broad range lift capacity. As illustrated in FIGS. 7 and 10,
first angle of attack 72 is
continuous along the outer section of wing 18, second angle of attack 74 is
continuous along the
midsection of wing 18, and third angle of attack 76 is continuous along the
inner section of wing
18. However, wing 18 may operate with one, two, or more angles of attack.
[0042] Referring to the embodiment in FIGS. 7 and 10-12, second angle of
attack 74 is the
steepest angle of attack on wing 18. Thus, second angle of attack provides the
maximum lift
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performance of hydrofoil 10 when the water flowing across wing 18 is flowing
at low speeds.
First angle of attack 72 is flatter than second angle of attack 74 and
provides maximum lift
performance of hydrofoil 10 when water is flowing across wing 18 at medium-to-
high speeds.
Third angle of attack 76 is flatter than first and second angles of attack 72
and 74. Thus, third
angle of attack 76 provides the maximum lift performance of hydrofoil 10 when
water is flowing
across wing 18 at high speeds, as well as providing some lift of yoke 16 at
lower speeds.
Although wings 18 have angles of attack providing maximum lift for differing
speeds of
hydrofoil 10, each angle of attack provides lift at speeds outside of the
particularly identified
angle of attack.
[0043] Illustrated in FIG. 7, when viewed continuously from wing tip 64 to
root 66, there are
at least two angle of attack transition points 80. Angle of attack transition
points 80 comprise a
plurality of incremental angles of attack, or wing twist, wherein each retains
the cross-sectional
configuration of the true hydrofoil. Thus, angle of attack 72 transitions to
angle of attack 74
through angle of attack transition point 80, and angle of attack 74
transitions to angle of attack 76
through another angle of attack transition point 80. Accordingly, wing 18
defines a plurality of
angles of attack from wing tip 64 to root 66. Using the example of the Speers
H105 hydrofoil,
the cross-sectional area will remain that of the H105 shape. This provides for
a broad range of
lift capacity across a broad range of speeds.
[0044] The embodiment illustrated in FIGS. 7 and 10 shows an angle of attack
72 of about
0.5 degrees. This same embodiment, illustrated in FIGS. 7 and 11, shows an
angle of attack 74
of about 2.5 degrees. And, this same embodiment, illustrated in FIGS. 7 and
12, shows an angle
of attack 76 of about zero (0) degrees. A maximum range for angle of attack 72
is between about
zero (0) degrees and about 5 degrees. A maximum range for angle of attack 74
is between about
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zero (0) degrees and about 20 degrees. A maximum range for angle of attack 76
is between
about zero (0) degrees and 10 degrees.
[0045] As illustrated in FIGS. 1-5, wings 18 have a swept-back configuration.
Near root 66,
wings 18 have forward section 82 seamlessly extending from yoke 16. Forward
section 82
sharply sweeps back from yoke 16 towards aft 28, and transitions into outer
section 84 near
transition point 80.
[0046] Yoke 16 is secured to cavitation plate 12 with securing devices (not
shown), which
may be setscrews or other similar low-profile devices. As illustrated in FIGS.
5, 6 and 9, a
plurality of threaded holes 86 are disposed through center body 20 of yoke 16.
Threaded holes
86 have threads 87 disposed therein. Threaded holes 86 are positioned to align
with edge 88 of
cavitation plate 12 when yoke 16 is positioned thereon. Once yoke 16 is
positioned on cavitation
plate 12, the securing devices are tightened until the yoke is securely
affixed to edge 88.
Preferably, securing devices compressively engage edge 88 of cavitation plate
12. By using
compressive force to secure yoke 16, the securing devices are non-invasively
securing yoke 16 to
cavitation plate 12. If additional and/or supplement support is desired, a low-
profile retention
strap 89, or another connective device (not shown), may be added, as
illustrated in FIGS. 15A-D.
If used, low-profile retention strap 89 is connected between sides 30, across
front 26 and
longitudinal channel 22, across bottom 34 and longitudinal channel 22, or a
combination thereof.
These two different combinations are illustrated in FIGS. 15A and 15B, and in
FIGS. 15C and
15D, respectively. Other connective devices may also be utilized to secure
hydrofoil 10 to
cavitation plate 12, such as, but not limited to devices positioned within
recessed attachment
points (not shown) on yoke 16.
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[0047] To reduce drag, exposed outer surface 90 of hydrofoil 10 is textured.
The preferred
texturing reduces the magnitude of turbulent separation of the water from
exposed outer surface
90. By reducing the magnitude of the turbulent separation, the localized drag
hydrofoil 10 is
subjected to is also reduced. In one embodiment, exposed outer surface 90 is
comprised of a
plurality of extremely small outward projections (not shown) that have varying
height and
placement across exposed outer surface 90, thereby creating the drag reducing
surface. This
approach is analogous to the denticles found on sharkskin. Preferably, the
drag reducing texture
of exposed outer surface 90 is formed thereon, but it may also be applied
thereto.
[0048] If desired, the entire exposed outer surface 90 of hydrofoil 10 may
have the drag
reducing texture. Alternatively, only particular segments of hydrofoil 10 may
have the drag
reducing texture. For example, the drag reducing texture on exposed outer
surface 90 may be
limited to upper surface 92 of tail section 24 and to wing upper surface 94 of
wings 18.
[0049] During performance of a boat having hydrofoil 10 installed thereon,
different sections
of hydrofoil 10 operate to provide lift. For example, for a boat at a full-
stop condition through
low speeds, the lifting body section of hydrofoil 10 at angles of attack 74
and 76 provide
increased lift. As that same boat accelerates, the lifting body sections of
hydrofoil 10 at angles
of attack 72 and 74 lift hydrofoil 10 in the water. The result is that the
lifting body sections of
hydrofoil 10 at angles of attack 72 and 74 provide for stabilization and lift
at higher speeds. The
lift provided by angle of attack 72 near wing tip 64 begins to carry the
majority of the lifting
while reducing the overall drag on hydrofoil 10 as the speeds increase.
[0050] In operation, water flowing over hydrofoil 10 transitions between
laminar and
turbulent. Turbulent flow creates drag and increases the profile drag, thereby
reducing the
performance of hydrofoil 10. By using wings 18 with a cross-sectional shape
configuration of
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the true hydrofoil, such as the Speers H105, the transition phase of the
laminar-to-turbulent is
such that the overall amount of laminar flow remains constant across wings 18
as the speed
varies. That is, as the speed increases, the laminar-to-turbulent transition
on wing upper surface
94 moves toward leading edge 60, while the laminar-to-turbulent transition on
wing lower
surface 96 moves toward trailing edge 62. This action keeps cavitation to a
minimum and
constant level, thereby minimizing and/or reducing drag. The addition of drag
reducing texture
to exposed outer surface 90 reduces the impact of the turbulent flow aft of
the laminar-to-
turbulent transition on wing upper surface 94, and/or wing lower surface 96.
Thus, the localized
drag and the overall drag are reduced, resulting in increased performance.
[0051] Other embodiments of the current invention will be apparent to those
skilled in the art
from a consideration of this specification or practice of the invention
disclosed herein. Thus, the
foregoing specification is considered merely exemplary of the current
invention with the true
scope thereof being defined by the following claims.
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