U.S. patent application number 12/049262 was filed with the patent office on 2008-12-11 for towed personal watercraft.
Invention is credited to Keith M. Rosiello.
Application Number | 20080305698 12/049262 |
Document ID | / |
Family ID | 40096309 |
Filed Date | 2008-12-11 |
United States Patent
Application |
20080305698 |
Kind Code |
A1 |
Rosiello; Keith M. |
December 11, 2008 |
TOWED PERSONAL WATERCRAFT
Abstract
A towed personal watercraft apparatus includes a submergible
unit and a platform. The submergible unit comprises at least two
independent vertical stabilizers and one or more hydrofoil units
mounted to at least one of the vertical stabilizers. One or more of
the hydrofoil units is pivotally attached to the vertical
stabilizers. Pivotal attachment can include a torsion spring or
roller bearing to allow the hydrofoil units to pivot or rotate
about the pitch axis of the platform, thereby improving stability
of the towed personal watercraft. Rotation of the hydrofoil units
can be limited for functional concerns and performance. For
example, rotation of the hydrofoils about the pivot can be allowed
in a first direction to prevent a nose dive, while being restricted
in a second direction to facilitate a launch of the watercraft out
of the water. The platform includes a user mount, such as foot
holds or equivalents.
Inventors: |
Rosiello; Keith M.;
(Shrewsbury, MA) |
Correspondence
Address: |
FOLEY & LARDNER LLP
111 HUNTINGTON AVENUE, 26TH FLOOR
BOSTON
MA
02199-7610
US
|
Family ID: |
40096309 |
Appl. No.: |
12/049262 |
Filed: |
March 14, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60894782 |
Mar 14, 2007 |
|
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Current U.S.
Class: |
441/79 |
Current CPC
Class: |
B63B 1/24 20130101; B63B
32/20 20200201 |
Class at
Publication: |
441/79 |
International
Class: |
B63B 35/73 20060101
B63B035/73 |
Claims
1. A towed personal watercraft apparatus, comprising: (a) an
elongated platform having a top surface, a bottom surface and a
platform major axis, wherein the top surface and the bottom surface
are substantially parallel, and the platform major axis lies in a
plane substantially parallel to the platform top surface and the
platform bottom surface, and substantially aligned with the largest
platform dimension; (b) one or more vertical stabilizers rigidly
attached to the elongated platform at least one of the one or more
vertical stabilizers having a set of two substantially parallel
vertical stabilizer side planes, wherein: (i) the platform major
axis lies approximately in each set of the two vertical stabilizer
side planes associated with the one or more vertical stabilizers,
and (ii) each set of the two vertical stabilizer side planes
associated with the one or more vertical stabilizers is
substantially perpendicular to the platform top plane and the
platform bottom plane; (c) one or more hydrofoils pivotally
attached to at one of the one or more vertical stabilizers; and (d)
one or more hydrofoils rigidly attached to at least one of the one
or more vertical stabilizers.
2. The apparatus of claim 1, further comprising one of a resilient
member and a bearing providing for rotation of the first subset of
the one or more hydrofoils about a pitch axis substantially
perpendicular to each set of the two vertical stabilizer side
planes associated with the one or more vertical stabilizers.
3. The apparatus of claim 1, wherein the resilient member is
selected from the group consisting of: a resilient material; a
torsion spring, a coil spring, a leaf spring; and combinations
thereof.
4. The apparatus of claim 2, wherein the rotation of the first
subset of the one or more hydrofoils is limited by one or more of
an upper stop and a lower stop.
5. The apparatus of claim 4, wherein the one or more of the upper
stop and the lower stop are rigidly affixed to the one or more
vertical stabilizers.
6. The apparatus of claim 4, wherein the rotation of the first
subset of the one or more hydrofoils is limited by an upper stop of
the one more of the upper stop and lower stop such that an angle
between the first subset of the one or more hydrofoils and the
platform major axis is greater than approximately -5 degrees.
7. The apparatus of claim 4, wherein the rotation of the first
subset of the one or more hydrofoils is limited by a lower stop of
the one or more of the upper stop and the lower stop such that the
angle between the first subset of the one or more hydrofoils and
the platform major axis is less than approximately +90 degrees.
8. The apparatus of claim 2, wherein the provided for rotation of
the first subset of the one or more hydrofoils approximately aligns
the first subset of the one or more hydrofoils to a fluid flow
vector in a reference frame centered at the pivot.
9. The apparatus of claim 2, wherein the providing for rotation of
the first subset of the one or more hydrofoils stabilizes the
platform about the pitch axis.
10. The apparatus of claim 1, wherein the one or more hydrofoils
provide a lift force for the platform.
11. The apparatus of claim 10, wherein the lift force is greater
for a third subset of one or more aft hydrofoils than for a fourth
subset of one or more forward hydrofoils. are rigidly attached to
the one or more vertical stabilizers.
12. The apparatus of claim 2, wherein each of the one or more
hydrofoils comprises a pair of hydrofoils substantially symmetric
about a plane parallel to the vertical stabilizer side planes.
13. The apparatus of claim 1, wherein each of the one or more
hydrofoils comprises a respective lateral termination feature.
14. The apparatus of claim 13, wherein the lateral termination
feature is approximately cylindrical with a radius greater than
approximately two times a distance between the vertical stabilizer
side planes.
15. The apparatus of claim 13, wherein the lateral termination
feature is configured to reduce a formation of air bubbles on or
near the one or more hydrofoils and reduces a turbulence at or near
the one or more hydrofoils.
16. The apparatus of claim 12, wherein one or more of the pair of
hydrofoils rotate independently about the pivot.
17. The apparatus of claim 1, wherein the one or more vertical
stabilizers minimize a resistance to fluid flow.
18. The apparatus of claim 1, wherein the one or more vertical
stabilizers stabilizes the platform about a pitch axis
substantially parallel to the platform major axis.
19. The apparatus of claim 1, wherein the platform further
comprises an operator interface.
20. The apparatus of claim 19, wherein the operator interface is
selected from a group consisting of a foot hold, a toe hold, a hand
hold, a seat, and combinations thereof.
Description
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS
[0001] The following non-provisional application follows
provisional application 60/894,782, filed Mar. 14, 2007, Attorney
Docket No. 350932-0106, which is incorporated herein by reference
in its entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to a marine apparatus.
Specifically, the present invention relates to a towed personal
watercraft apparatus.
BACKGROUND OF THE INVENTION
[0003] Standard rigid towed personal watercraft, designed for
standing or kneeling, such as waters skis, water toboggans, ski
boards, and wake boards, ride on the surface of the water, and as a
result, are subjected to high drag forces and surface roughness.
Towed personal watercraft drag forces can be reduced and surface
roughness issues mitigated by reducing or eliminating contact with
the water's surface. To this end, a variety of towed personal
watercraft have been fitted with lift elements, commonly called
hydrofoils, to allow the body of the towed personal watercraft to
ride above the water's surface, reducing drag and the effects of
surface roughness.
[0004] Hydrofoil design for towed personal watercraft differs from
hydrofoil design for larger, self-propelled watercraft. In earlier
models, stability in the critical pitch axis in larger watercraft
was maintained by a set of bow and stern hydrofoils that were
delta-shaped or U-shaped. Rotations of the watercraft in the pitch
axis were countered by an increase in lift force generated by the
newly submerged hydrofoil segments. The delta-shaped or U-shaped
hydrofoil, designed to lift self-propelled watercraft that weighed
hundreds or thousands of pounds, was more than adequate in
countering pitch deflections caused by passengers shifting weight.
This is not as true for a towed, personal watercraft, where the
weight of the passenger, or rider, is much greater than the
watercraft itself.
[0005] Delta-shaped or U-shaped hydrofoils designed for
self-propelled watercraft have given way to adjustable T-shaped
hydrofoils that function similar to an airplane's wing. As the
density of water is much greater than that or air, the pitch
stability for the T-shaped hydrofoil is much more sensitive than
pitch stability for an airplane's wing, and as such the angle of
attack of each hydrofoil must be constantly adjusted by computer
control. Computer controlled towed personal watercraft are
obviously not a practical option for towed personal watercraft.
[0006] Several single-hydrofoil personal watercraft have been
developed, for towed and wind-powered watercraft. Typically, these
watercraft require tremendous skill and balance. None are stable;
that is, none have a restoring force to counteract pitch
deflections in the body of the towed personal watercraft.
SUMMARY OF THE INVENTION
[0007] The present invention fulfills needs present in the art by
providing a towed personal watercraft apparatus where drag forces
are reduced, surface roughness issues are mitigated, and pitch
instabilities found in the present art are practically eliminated.
To accomplish each of these objectives simultaneously, a torsion
spring-mounted forward hydrofoil assembly, herein referred to as a
canard assembly, in an embodiment of the present invention provides
a restoring lift force and torque to counteract pitch deflections
in the body of the towed personal watercraft.
[0008] A towed personal watercraft apparatus comprises a platform,
one or more vertical stabilizers, and one or more hydrofoils
attached to the one or more vertical stabilizers. The platform
comprises a platform top surface, a platform bottom surface, and a
platform major axis, wherein the platform top plane and the
platform bottom plane are substantially parallel. The platform
major axis is aligned approximately parallel to the largest
platform dimension of the platform top surface and the platform
bottom surface.
[0009] In some embodiments, each of the one or more vertical
stabilizers comprises a pair of two substantially parallel
stabilizer surfaces, wherein the platform major axis lies in a
plane substantially parallel to each pair of stabilizer side
surfaces associated with the one or more vertical stabilizers, and
each set of the two vertical stabilizer side planes associated with
the one or more vertical stabilizers is substantially perpendicular
to the platform top plane and the platform bottom plane.
[0010] A first subset of the one or more hydrofoils are attached to
the one or more vertical stabilizers pivotally. Pivotal attachment
can include one of a spring and a bearing. A second subset of the
one or more hydrofoils are rigidly attached to the one or more
vertical stabilizers. One of a spring and a bearing provide for
rotation of the first subset of the one or more hydrofoils about a
pitch axis substantially perpendicular to each pair of stabilizer
surfaces associated with the one or more vertical stabilizers. The
spring can be one of a torsion spring, a coil spring, a leaf
spring, a resilient material, and combinations of these.
[0011] A rotation of the first subset of the one or more hydrofoils
is limited by one or more of an upper stop and a lower stop. In
some embodiments, the upper stop and the lower stop are rigidly
affixed to the one or more vertical stabilizers. The rotation angle
between the first subset of the one or more hydrofoils and the
platform major axis is limited to a range of between about -5
degrees and +90 degrees.
[0012] A rotation of the first subset of the one or more hydrofoils
approximately aligns the first subset of the one or more hydrofoils
to a fluid flow vector in a reference frame centered at the one of
a spring and bearing. Providing for rotation of the first subset of
the one or more hydrofoils stabilizes the platform about the pitch
axis.
[0013] Pitch stability is a critical design issue. Rigidly mounting
one or more hydrofoils forward of the platform center of mass
results in pitch instability. That is, pitching a front end of the
platform up urges the hydrofoil to a greater angle of attack,
increasing the forward lift, further increasing the pitch.
Similarly, pitching down a front end of the platform urges the
hydrofoil to a reduced angle of attack, reducing lift and
increasing drag, further reducing pitch. Pitch attitude transients
can be introduced by weight shifts of an operator or water
turbulence.
[0014] A canard assembly comprises a subset of the first subset of
the one or more hydrofoils free to rotate, which are herein
designated as rotatable hydrofoils, the one of a spring and a
bearing, and the upper and lower stops, wherein each of the
elements of the canard assembly reside forward of the platform
center of mass. To address pitch instabilities, the rotatable
hydrofoils of the canard assembly in the present invention are
designed to align to the fluid flow vector. In some embodiments,
this rotation is also based on torques about the pivot due to a
resilient member, such as a torsion spring, storing energy in the
torsion spring. The torsion spring is rigidly affixed to a vertical
stabilizer; the vertical stabilizer is rigidly attached to the
platform of the towed personal watercraft.
[0015] The rotatable hydrofoils are provided a nearly constant
angle of attack by the canard assembly. This is in sharp contrast
with the one or more hydrofoils rigidly attached to the one or more
vertical stabilizers, where the angle of attack is fixed to the
pitch of the platform.
[0016] The center of lift of the rotatable hydrofoils lies on or
near a pivot axis of the canard assembly; the pivot axis of the
canard assembly is approximately collinear with a rotation axis of
the one of a spring and a bearing. Nominally, the lift and drag
forces imparted to the rotatable hydrofoils by the fluid
streamlines produce a lift force along the canard assembly pivot
axis with little of no torsion spring deflection. The term fluid
streamline refers to the fluid flow across a hydrofoil surface; the
term fluid flow vector is reserved for the relative velocity
component of the fluid flow with respect to the platform.
[0017] Pitch transients in the platform of the towed personal
watercraft do not rotate the canard assembly with respect to a
fluid flow vector. Thus, the hydraulic force dampens canard
assembly rotation for any appreciable towed velocity. A vertical
velocity component associated with a pitch rate momentarily changes
the rotatable hydrofoils effective angle of attack, providing a
short lift force pulse that resists the pitch transient just before
the rotatable hydrofoils is able to realign with the new fluid flow
vector. When the vertical velocity component is removed, the
torsion spring remains deflected by the angular difference in the
pitch of the platform of the towed personal watercraft and the
fluid flow vector. The torsion spring provides a restoring torque
to counteract the pitch transient in the platform of the towed
personal watercraft. As a result, the towed personal watercraft in
the present invention can ride above the water's surface, reducing
drag and the effects of surface roughness, without suffering the
pitch instabilities of similar towed personal watercraft in the
present art.
[0018] In some embodiments, a lift force is greater for a third
subset of one or more aft hydrofoils than for a fourth subset of
one or more forward hydrofoils. This arrangement is beneficial for
embodiments in which most of the operator's weight or force is
imparted on the aft portion of the platform.
[0019] In some embodiments, each of the one or more hydrofoils
comprise a pair of hydrofoils substantially symmetric about a plane
parallel to the pair of vertical stabilizer surfaces. One or more
of the pair of hydrofoils may rotate independently.
[0020] In some embodiments, each of the one or more hydrofoils
comprises a lateral termination features. The lateral termination
feature can be approximately cylindrical with a radius greater than
approximately two times a distance between the vertical stabilizer
side planes. The lateral termination feature reduces a formation of
air bubbles on or near the one or more hydrofoils and reduces a
turbulence at or near the one or more hydrofoils.
[0021] The one or more vertical stabilizers minimize a resistance
to fluid flow and stabilizes the platform about a pitch axis
substantially parallel to the platform major axis.
[0022] The platform further comprises an operator interface. The
operator interface is one of a foot hold, a toe hold, a hand hold,
and a seat.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The accompanying drawings, which are incorporated herein and
from and form a part of the specification, illustrate the present
invention and, together with the description, further serve to
explain the principles of the invention and to enable a person
skilled in the pertinent art to make and use the invention.
[0024] FIGS. 1A-1D show a schematic of an embodiment of a towed
personal watercraft, in accordance with the present invention.
[0025] FIG. 2 shows a top/rear perspective of an embodiment of the
towed personal watercraft, shown in FIGS. 1A-1D, in accordance with
the present invention.
[0026] FIG. 3 shows a schematic of an embodiment of a canard
assembly of the towed personal watercraft, in accordance with the
present invention.
[0027] FIG. 4A shows an embodiment of the towed personal watercraft
pitched downward, with no limit on the rotation of an exemplary
rotatable hydrofoil, in accordance with the present invention.
[0028] FIG. 4B shows an embodiment of the towed personal watercraft
pitched upward, with a limit on the rotation of an exemplary
rotatable hydrofoil, in accordance with the present invention.
[0029] FIG. 5 shows a dimensioned side view of one embodiment of
the towed personal watercraft, in accordance with the present
invention.
[0030] FIG. 6 shows a dimensioned top view of one embodiment of the
towed personal watercraft, in accordance with the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0031] It should be appreciated that the particular implementations
shown and described herein are examples of the present invention
and are not intended to otherwise limit the scope of the present
invention in any way. Further, the techniques are suitable for
applications in marine systems, hydraulics systems, aeronautic and
aerospace systems, wind tunnel systems, or any other
application.
[0032] The present invention is an improved, towed personal
watercraft apparatus. A canard assembly comprising a forward pair
of rotatable hydrofoils pivotally attached to a vertical
stabilizer, the vertical stabilizer itself rigidly affixed to the
platform of the towed personal watercraft, is configured to provide
a restoring lift force or torque to counteract pitch transients of
the platform resulting from operator weight shifts or water
turbulence. In a representative embodiment, a rotation axis of a
torsion spring pivotally attached to the rotatable hydrofoils is
positioned at or near the center of lift of the canard
assembly.
[0033] FIGS. 1A-1D show a schematic of an embodiment of a towed
personal watercraft (100), in accordance with the present
invention. The towed personal watercraft is subdivided into the
following two units for descriptive purposes: a submergible unit
(101), which provides lift, and a platform (151), which allows for
an operator to ride the towed personal watercraft (100).
[0034] The submergible unit (101) comprises a canard assembly
(110), which is attached to a forward vertical stabilizer (120). In
some embodiments, a forward hydrofoil (121) is rigidly affixed to
the forward vertical stabilizer (120) at or near the bottom of the
forward vertical stabilizer (120). The submergible unit further
comprises an aft vertical stabilizer (130), which is attended by an
aft hydrofoil (131) rigidly affixed to the aft vertical stabilizer
(130) at or near the bottom of the aft vertical stabilizer
(131).
[0035] Submergible unit (101) forward and aft vertical stabilizers
(120, 130) provide for minimum resistance to water flow in an
intended direction and provide for lateral stability, resisting
roll, rotation of the platform (151) about its major axis. In
another embodiment, the forward hydrofoil (121) is not present.
[0036] In the exemplary embodiment, both of the forward hydrofoils
(121) and aft hydrofoil (131) are comprised of two symmetric
sections, extending laterally and slightly aft of their respective
forward and aft vertical stabilizers (120, 130), substantially
parallel to the platform (151). In another embodiment, at least one
of the forward hydrofoil (121) and aft hydrofoil (131) are not
parallel to the platform (151), but rather extend downward, forming
an inverted `V`. The inverted `V` configuration allows for a lift
force surface area to vary as the towed personal watercraft
submersion changes. Each of the two symmetric sections for both the
forward hydrofoil (121) and aft hydrofoil (131) comprise a lateral
termination feature (140), a cylindrical extension with radius
greater than twice the width of the hydrofoil in which they are
mounted. The lateral termination feature (140) minimizes the
formation of air bubbles on the hydrofoil surfaces and reduces
turbulence near the hydrofoil surfaces, allowing for greater
lift.
[0037] Both the forward and aft hydrofoils (121, 131) provide
lateral stability and lift to the platform (151). The surface area
of the aft hydrofoil (131) is greater than that of the forward
hydrofoil (121), generating greater lift and stability than the
forward portion of the platform (151). The aft portion of the
platform (151) supported the majority of the operator's weight. The
aft hydrofoil (131) affixed to the bottom of the aft vertical
stabilizer (130) is a greater distance from the platform (151) than
the forward hydrofoil (121) affixed to the bottom of the forward
vertical stabilizer (120).
[0038] Both of the submergible unit (101) forward and aft vertical
stabilizers (120,130) are rigidly affixed to a towed personal
watercraft body, or ski (152), an element of the platform (151).
The ski (152) comprises a ski top surface (152a) and a parallel ski
bottom surface (152b). The ski top surface (152a) and ski bottom
surface (152b) are joined at their respective boundary edges by one
or more substantially curved surfaces.
[0039] Additionally, the ski (152) comprises an operator interface,
such as a series of operator holds. In the present embodiment, the
ski comprises a set of foot holds (153, 154). The ski top surface
(152a) supports an operator; the foot holds (153, 154) allow for
operator control. The ski bottom surface (152b) provides an initial
water interface. The ski bottom surface (152b) releases from the
water at a speed sufficient for submerged unit (101) elements 110,
121, and 131 to generate the necessary lift to overcome the weight
of the operator, the weight of the platform (151), the surface
tension of the water surface, and the weight of the submerged unit
(101) less the buoyant force of the submerged unit (101).
[0040] In some embodiments, the forward portions of both top ski
surface (152a) and bottom ski surface (152b) curve upward,
remaining parallel, away from the horizontal plane in which the
majority of the ski (152) lays. The aft portions of both top ski
surface (152a) and bottom ski surface (152b) also curve upward, but
to a significantly smaller degree than the forward portion. The
remaining portions of the top ski surface (152a) and bottom ski
surface (152b) do not deviate significantly from the aforementioned
horizontal plane, with the exception of a series of parallel
grooves (155), each approximately six inches in length, notched
into the most aft portion of the bottom ski surface, parallel to
the major axis of the ski (152). The parallel grooves (155) provide
control at the start of a tow.
[0041] In some embodiments, the towed personal watercraft (100) is
itself buoyant. The submerged unit (101) is neutrally buoyant or
not buoyant. A buoyant submerged unit would make it very difficult
for the operator to balance underwater prior to starting a tow. In
another embodiment, weight is added to the forward and aft vertical
stabilizers (120, 130) for ballast to resist an additional lift
force that accompanies an increase in platform velocity, raising
the vertical stabilizers above the water's surface. In a further
embodiment, the canard assembly (110) can be adjusted such that a
symmetric pair of rotatable hydrofoils are nominally set to a
higher angle of attack and allowed to rotate to a lower angle of
attack at increased platform velocities. In this way, the
additional lift force that accompanies an increase in platform
velocity for a fixed hydrofoil is reduced.
[0042] Suitable materials for each element of the submerged unit
(101) include, but are not limited to: composite materials such as
weighted fiberglass and weighted carbon-fiber epoxy, metals such as
aluminum and stainless steel, polymers, and combinations of these
materials. The platform (151) is buoyant. Suitable materials for
each element of the platform (151) excluding foot holds (153, 154)
include, but are not limited to: wood, epoxy, carbon-fiber epoxy,
metals, foam, plastics, and combinations of these materials.
Suitable materials for each foot hold (153, 154) include, but are
not limited to: rubber, leather, foam, plastics, and combinations
of these materials.
[0043] FIG. 2 shows a top/rear perspective of an embodiment of a
towed personal watercraft (200), in accordance with the present
invention. As with FIGS. 1A-1D, the towed personal watercraft is
subdivided into the following two units for descriptive purposes:
the submerged unit (101), which provides lift, and the platform
(151), which allows for an operator to ride the towed personal
watercraft (100). FIG. 2 numbering and description follow the
numbering and description given previously for FIGS. 1A-1D.
[0044] FIG. 3 shows a schematic of one embodiment of the canard
assembly (110) of the towed personal watercraft, in accordance with
the present invention. The canard assembly (110) includes a
symmetric pair of rotatable hydrofoils (221), a torsion spring
(211) that attaches the rotatable hydrofoils (221) to the forward
vertical stabilizer (120), and an upper and lower canard stop (212,
213), rigidly affixed to the forward vertical stabilizer (120), to
limit rotation of the rotatable hydrofoils (221).
[0045] Nominally, with a level platform (151), the lift and drag
forces imparted to the canard assembly (110) by the fluid
streamlines produce a lift force at a point at near a canard
assembly pivot axis, which is approximately collinear with a
rotation axis of the torsion spring (211), with little of no
torsion spring deflection. The canard assembly (110) is designed to
rotate based on the hydraulic forces of the fluid flow over the
rotatable hydrofoils (221) and the torsion spring (211) attaching
the rotatable hydrofoils (221) to the forward vertical stabilizer
(120) rigidly affixed to the platform (151).
[0046] Pitch transients in the platform (151) do not rotate the
canard assembly (110) with respect to the fluid flow vector; the
hydraulic force of the streamlines damps the canard assembly (110)
rotation for any appreciable velocity. The vertical velocity
component associated with the pitch rate changes the rotatable
hydrofoils (221) effective angle of attack, momentarily providing a
lift force that resists the pitch transient before the canard
assembly (110) realigns with the new fluid flow vector. When the
vertical velocity component is removed, the torsion spring (211)
remains deflected by the angular difference in the pitch of the
body of the towed personal watercraft and the fluid flow vector. As
a result, the torsion spring (211) is deflected by the angular
difference in the pitch of the platform (151) and the fluid flow
vector. The torsion spring (211) provides a restoring torque to
counteract the pitch transient in the platform (151), returning the
platform (151) and torsion spring (211) to their respective nominal
positions.
[0047] Upper and lower canard stops (212, 213) are designed to
allow the rotatable hydrofoils (221) to rotate from an elevation
angle of 90 degrees, the upper stop (212) limit, down to an
elevation angle of -5 degrees, the lower stop (213) limit. The
upper stop (212) limit of 90 degrees allows the rotatable
hydrofoils (221) to follow the fluid streamlines in a steep dive
and to provide a momentary restoring lift through the rotatable
hydrofoils (221) and a restoring torque through the torsion spring
(211). The lower stop (213) limit of -5 degrees allows the
rotatable hydrofoils (221) to follow the platform pitch, which
increases the rotatable hydrofoils (221) angle of attack, providing
positive feedback for lifts in jumps and stunt execution.
[0048] In the present embodiment, the canard assembly (110)
symmetric pair of rotatable hydrofoils (221) rotate in tandem. In
another embodiment, the pair of rotatable hydrofoils (221) that
comprise the canard assembly (110) rotate independently, each
attached to the forward vertical stabilizer (120) with independent
torsion springs (211).
[0049] In another embodiment, the canard assembly (110) is mounted
to the forward vertical stabilizer in a roller bearing housing,
free to rotate with no torsion spring (211) restoring torque. In
this embodiment, the lift force will be momentarily increased or
reduced as a function of platform (151) vertical velocity, which
effectively changes the angle of attack of the rotatable hydrofoils
(221). Following a pitch or vertical velocity transient, the
rotatable hydrofoils (221) will return to their nominal angle of
attack, following the fluid flow vector, without imparting a
restoring torque. The canard assembly (110), without the torsion
spring (211), is marginally stable. The canard assembly (110)
without the torsion spring (211) is not as stable as with the
torsion spring (211), as it does not produce a restoring
torque.
[0050] The towed personal watercraft in the preferred embodiment is
stable, and as such, can ride above the water's surface, reducing
drag and the effects of surface roughness, without suffering the
pitch instabilities of similar towed personal watercraft in the
present art.
[0051] FIG. 4A shows an embodiment of the towed personal watercraft
(100) pitched downward, with no limit on the rotation on an
exemplary rotatable hydrofoil, in accordance with the present
invention. The rotatable hydrofoils (221) align with the fluid flow
vector such that the angular spring deflection is approximately
equal to the negative pitch. The angle of attack remains
approximately constant, approximately equal to the angle of attack
in a level pitch state.
[0052] FIG. 4B shows an embodiment of the towed personal watercraft
pitched upward, with a limit on the rotation on an exemplary
rotatable hydrofoil, in accordance with the present invention. The
rotatable hydrofoils (221) start to align with the fluid flow
vector, but are limited by the lower canard stop. In an embodiment,
the lower canard stop can be set to limit the rotatable hydrofoils
(221) to an angle of approximately -5 degrees. The resulting angle
of attack is the pitch angle minus plus the spring deflection, -5
degrees in the present embodiment, plus the angle of attack in a
level pitch state. The lower canard stop allows for a higher angle
of attack in pitch up maneuvers, giving extra lift for jumps and
tricks.
[0053] FIGS. 5 and 6 show dimensioned side and top views of one
embodiment of the towed personal watercraft, in accordance with the
present invention, and as such require no further explanation. One
or more of the dimensions can be varied for performance
enhancement, as a function of the operator size, weight, and
style.
[0054] While the invention has been described in connection with
the specific embodiments thereof, it will be understood that it is
capable of further modification. Furthermore, this application is
intended to cover any variations, uses, or adaptations of the
invention, including such departures from the present disclosure as
come within known or customary practice in the art to which the
invention pertains, and as fall within the scope of the appended
claims.
[0055] All publications, patents, and patent applications mentioned
in this specification are herein incorporated by reference to the
same extent as if each individual publication, patent, or patent
application was specifically and individually indicated to be
incorporated by reference.
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