Note: Descriptions are shown in the official language in which they were submitted.
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SYSTEM AND METHOD FOR MARINE PROPULSION WITH LOW ACOUSTIC
NOISE
BACKGROUND
Field of the Disclosure
[0001] This disclosure relates generally to systems for propelling marine
vessels relative to a
body of water and, more particularly, to low acoustic noise systems for
propelling a marine
vessel relative to a body of water.
Description of the Related Art
[0002] Marine propulsion refers to the mechanical means to impart motion to a
marine vessel
.. on or below the surface of water. Most commonly, some form of helical-screw
propeller is
rotated in the water by a motor or engine to generate thrust by increasing the
momentum of
the water. As a reaction to the thrust, the marine vessel is propelled.
SUMMARY
[0003] Embodiments disclosed herein may be generally directed to a system for
increasing
the momentum of water for the purpose of propelling a marine vessel and a
system for
controlling the emission of the water to control a direction in which the
marine vessel is to be
propelled.
[0004] Impeller discs may be more efficient than screw-type impeller discs by
imparting
radial momentum on the water as opposed to axial momentum. Embodiments of a
vertically
oriented impeller disc may be driven by an electric motor mounted on top of a
drive shaft
extending along the vertical axis. The design of the propulsion system,
including the design
of individual components or the arrangement of components may allow for slow
rotation of
the vertically oriented impeller disc to reduce the acoustic noise generated
in the water by
ensuring the tip speed of the impeller disc blades is maintained well below a
cavitation speed,
may direct any acoustic noise away from the water intake or exit ports to
minimize acoustic
noise transmitted to the ambient water, and may ensure any acoustic noise
exiting a marine
vessel is directed to minimize the range over which the acoustic noise may
affect marine
animals.
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[0005] Embodiments disclosed herein may be described as they pertain to a
ferry boat used to
transport passengers and cargo but may be useful in other applications with
other types of
marine vessels without departing in scope from the disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] For a more complete understanding of the invention and its features and
advantages,
reference is now made to the following description, taken in conjunction with
the
accompanying drawings, in which:
[0007] FIGURE 1 is a cutaway side view of an embodiment of marine vessel with
a
propulsion system configured for low noise propulsion of the marine vessel;
and
[0008] FIGURE 2 is a bottom view of the marine vessel of FIGURE 1, depicting a
portion of
one embodiment of a propulsion system with a water intake oriented in a
substantially
downward vertical direction;
[0009] FIGURE 3 is a cutaway bottom view of the marine vessel of FIGURE 1,
depicting a
portion of one embodiment of a propulsion system with a single vertically
oriented
centrifugal impeller disc configured for low noise propulsion; and
[0010] FIGURE 4 is a cutaway bottom view of a marine vessel, depicting a
portion of one
embodiment of a system configured with multiple vertically oriented
centrifugal impeller
discs in a single plenum chamber.
DESCRIPTION OF PARTICULAR EMBODIMENT(S)
[0011] In the following description, details are set forth by way of example
to facilitate
discussion of the disclosed subject matter. It should be apparent to a person
of ordinary skill
in the field, however, that the disclosed embodiments are exemplary and not
exhaustive of all
possible embodiments.
[0012] As used herein, a hyphenated form of a reference numeral refers to a
specific instance
of an element and the un-hyphenated form of the reference numeral refers to
the collective or
generic element. Thus, for example, control gate "132-1" refers to an instance
of a control
gate, which may be referred to collectively as control gates "132" and any one
of which may
be referred to generically as control gate "132."
[0013] For the purposes of this disclosure, a marine vessel may refer to a
boat, a ship, a
submarine or other form of transportation in a body of water.
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[0014] The architecture and design of many marine vessels is based primarily
on propelling
the marine vessel efficiently across large distances in a body of water.
However, situations
exist that marine vessel designs are challenged to accommodate. In particular,
several
challenges of existing marine vessel designs are associated with the use of a
screw-type
propeller system oriented in a forward-aft plane.
[0015] A challenge with the design and operation of screw propellers is the
generation of
high levels of broadband acoustic noise. Acoustic noise may be generated by
the shape or
design of a screw propeller and the operation of a power source associated
with the propeller.
Ongoing scientific research indicates acoustic noise may adversely affect
marine animals and
may be especially detrimental to certain species such as whales. High levels
of acoustic noise
may travel over long distances.
[0016] As another challenge, the operation of screw propellers operating near
the maximum
rotational speed results in large losses in efficiency due to friction forces
on the propeller
blades, adiabatic compression and consequential heating of water near the
propeller blades
and acoustic pressure waves radiating from the propeller.
[0017] As another challenge, in many marine vessel designs, a single propeller
is mounted at
a fixed angle in a forward-aft plane and a rudder is positioned aft of the
propeller to steer the
marine vessel. By turning the rudder, the direction of momentum of the water
is changed, but
with a loss of energy in the water. Some marine vessels, notably ferries, have
multiple
propellers mounted on rotatable vertical shafts that enable directional
changes of momentum
of the water. The ability to generate thrust at each propeller may be
beneficial for delicate
maneuvering of a ferry near a dock, but these systems are complex.
[0018] As another challenge, in many marine vessel designs, the position of
the propeller is
below most, if not all, other parts of the marine vessel for reduced impedance
of water being
draw in into the propeller. This low position of the propeller exposes the
propeller to the risk
of fouling by seaweed, rope or other debris present below the surface of the
water, which may
not be visible to a person on the marine vessel. A propeller may be damaged by
contact with
a seabed, a reef or some other surface at the bottom of the body of water.
[0019] As another challenge, in many marine vessel designs, exposed propellers
present a
safety hazard to marine life. There is evidence that marine mammals have been
injured as
they were swimming near the surface or surfaced to breathe. Seaweed and other
plant life
may be entangled in a propeller and pulled out of the seabed.
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[0020] To overcome these problems with marine vessels and prevent or mitigate
negative
environmental effects associated with marine vessels, embodiments disclosed
herein
comprise a propulsion system configured with an impeller disc rotatable about
a vertical axis
to entrain water in a direction independent of a speed or direction of travel
of the marine
vessel and accelerate the water in a radial direction, wherein a plurality of
control gates
arranged around the hull may be selectively opened and closed to propel the
marine vessel.
Embodiments may operate at higher efficiencies with reduced acoustic noise and
a lower risk
to marine wildlife and the environment.
[0021] Turning to the drawings, FIGURE 1 illustrates a side view depicting a
vertical section
of marine vessel 100 from bow to stern. Marine vessel 100 comprises an outer
hull 110
configured to be at least partially submerged in a body of water. In some
embodiments, one
or more decks 112 and a bridge 114 may be located above the surface of the
body of water.
In some embodiments, marine vessel 100 may be configured with hull 110 at
least partially
submerged in the body of water. FIGURE 1 depicts one embodiment of marine
vessel 100 as
a ferry boat with hull 110 configured as a substantially straight surface from
the bow to the
stern. Hull 110 may be configured with a flat bottom.
[0022] Marine vessel 100 comprises propulsion system 120 configured to be at
least partially
submerged in the body of water. Propulsion system 120 comprises water intake
122, impeller
disc 124 rotatable about vertical axis 126 and located in plenum chamber 128,
electric motor
130 for rotating impeller disc 124 about vertical axis 126, a plurality of
control gates 132
located near the periphery of hull 110, and control system 150 for controlling
rotational speed
of impeller disc 124 and selectively opening and closing one or more control
gates 132
directing water through ports 137 in the hull to steer marine vessel 100.
Marine vessel 100
may include batteries 148 for supplying electric power to electric motor 130
for rotating drive
shaft 147 about vertical axis 126 or to one or more control gates 132.
[0023] Water intake 122 comprises one or more openings formed in hull 110 to
allow a
desired volumetric flow rate of water entering propulsion system 120 but at a
reduced
velocity. Marine vessel 100 may be configured with a buoyancy to ensure marine
vessel 100
is partially submerged in the body of water with water intake 122 always below
the surface of
the body of water. In this configuration, water intake 122 may ensure a
volumetric flow rate
of water is naturally biased into propulsion system 120. Reducing the velocity
of water
entering propulsion system 120 may reduce the risk of debris, plants and
animals from
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entering propulsion system 120 and may further reduce turbulence of water to
reduce
acoustic noise. In some embodiments, marine vessel 100 may be designed such
that water
intake 122 is always a minimum depth below the water surface, discussed in
greater detail
below.
[0024] Water intake 122 may be configured to reduce the effects that water
intake 122 has on
marine vessel 100 moving in the body of water as well as the effects that
entraining water
through water intake 122 has on marine vessel 100 moving in the body of water.
For
example, water intake 122 formed substantially parallel with respect to hull
110 may reduce
the effects that a speed of marine vessel 100 has on a velocity of water
entering water intake
122 and may also reduce the possibility of debris or animals entering water
intake 122. In
some embodiments, water intake 122 may be formed in hull 110 and oriented in a
direction
relative to a direction of travel of marine vessel 100. For example, water
intake 122 may be
formed in hull 110 and oriented substantially perpendicular to a direction of
travel of marine
vessel 100 to reduce the possibility of debris or animals entering water
intake 122.
[0025] In some embodiments, water intake 122 oriented substantially downward
with respect
to hull 110 may direct any acoustic noise emitted by propulsion system 120
downward (i.e.,
in an axial direction relative to vertical axis 126), which may reduce the
distance that acoustic
noise can travel outward (i.e., in a radial direction relative to vertical
axis 126).
[0026] One or more of the location, size and shape of water intake 122 may be
configured to
improve stability of marine vessel 100 or provide for greater safety or less
acoustic noise. In
some embodiments, water intake 122 may be located at or near the lowest point
of hull 110
and centrally located between the bow and stern to allow marine vessel 100 to
approach a
shore without a propeller contacting a bottom surface of the body of water. In
some
embodiments, water intake 122 may be formed near a keel of hull 110 and
oriented in a
downward direction, minimizing the possibility that people or debris falling
off a deck of
marine vessel 100 can be drawn into water intake 122. In some embodiments,
water intake
122 may be formed to minimize pressure variations associated with rotation of
impeller disc
124.
[0027] Referring to FIGURES 1 and 2, in some embodiments, water intake 122 may
comprise a plurality of inlet ports 123 formed in hull 110. The shape, size
and orientation of
inlet ports 123 may be selected to maximize surface area of water inlet 122 to
allow a desired
volumetric flow rate of water into propulsion, reduce drag on marine vessel
100 due to water
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flowing past water intake, reduce local pressure buildup associated with blade
passing tone
(BPT), minimize the size of marine life that can enter water intake 122 or
some other factor.
In some embodiments, water intake 122 may be formed as a single opening and
covered by a
mesh or grate to prevent marine life or debris from entering water intake 122.
Advantageously, a mesh or grate covering water intake 122 may be configured to
limit the
size of items from entering water intake 122 without affecting the volumetric
flow rate of
water entering water intake.
[0028] Referring still to FIGURE 1, impeller disc 124 is positioned in plenum
chamber 128
and rotatable about vertical axis 126. Impeller disc 124 may be shaped to
efficiently increase
the momentum of water and direct the water radially outward while minimizing
or preventing
pressure waves. In some embodiments, impeller disc 124 may be formed with a
large
diameter top surface 134, a smaller diameter bottom surface 135 and an angled
surface 136
connected to top surface 134 and bottom surface 135, wherein top surface 134
may be
considered as the base and angled surface 136 may be considered as the side.
Top surface
134 extends radially outward to an outer edge 138 with a large outer diameter.
Top surface
134 may be substantially flat or have a curvature formed to outer edge 138.
Bottom surface
135 may have a smaller outer diameter and be separated from top surface 134 by
a distance,
wherein the distance corresponds to a height of impeller disc 124.
[0029] Angled surface 136 may be straight or comprise a curvature between the
most radially
inward edge of angled surface 136 and the most radially outward edge of angled
surface 136.
Referring to FIGURE 1, angled surface 136 may have a generally straight cross-
section
profile, wherein impeller disc 124 may resemble a frustro-conical shape. In
other
embodiments (not shown), angled surface 136 may have a curved cross-section
profile. A
curved cross-section profile may be based on a simple curve or a complex
curve. For
example, angled surface 136 may have a cross-section profile based on a
tractrix. Other
cross-section profiles may be possible.
[0030] Angled surface 136 comprises a plurality of blades 140 shaped to move
water radially
outward as impeller disc 124 rotates. As depicted in FIGURE 1, blades 140 may
be formed
as substantially curved radially structures of constant height or thickness.
Referring to one or
more of FIGURES 2-4, blades 140 may also be formed as curved structures with
or without
constant height or thickness. For example, in some embodiments (not shown),
blades 140
may be formed as curved structures based on the involute of a circle.
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[0031] In some embodiments, impeller disc 124 may be formed to have a neutral
or positive
buoyancy. For example, impeller disc 124 may be formed with an enclosed hollow
structure
filled with air or some other fluid having a lower density than water. In some
embodiments,
impeller disc 124 may be configured as an enclosed hollow structure with an
outer diameter
greater than a portion of the width of hull 110. For example, impeller disc
124 may be
configured with outer edge 138 of top surface 134 having an outer diameter
greater than 25%,
50% or 60% of a width of hull 110, wherein a large hollow structure filled
with air may
provide buoyancy when marine vessel 100 is at least partially submerged in
water.
[0032] Impeller disc 124 may be formed with a structure such that power needed
to move
water through propulsion system 120 is substantially based on the density of
the water. For
example, impeller disc 124 may comprise an enclosed hollow structure formed
from a
lightweight, high strength material, wherein the power needed to rotate
impeller disc 124
alone is much less than the power needed to move water through propulsion
system 120.
[0033] Impeller disc 124 may have a base-height ratio selected for efficiently
raising water
.. and increasing momentum of the water through propulsion system 120. In some
embodiments, impeller disc 124 may be configured with a large diameter and a
relatively
small height. In these configurations, electric motor 130 may be configured to
generate
rotational power with a high torque and a low rotational speed to raise and
accelerate water
radially outward. Electric motor 130 may efficiently rotate impeller disc 124
with reduced
acoustic noise as compared to diesel or other internal combustion engines. In
some
embodiments, impeller disc 124 formed as a hollow, lightweight structure with
a large base to
height ratio may require less power to rotate, wherein batteries 148 may
provide sufficient
electric power to electric motor 130 and control gates 132 to propel marine
vessel 100.
[0034] Rotation of impeller disc 124 about vertical axis 126 may help
stabilize marine vessel
100. In some configurations, impeller disc 124 rotating about vertical axis
126 may function
as a gyroscope, resisting forces that or reducing the amplitude of forces
exerted by waves on
hull 110. In some embodiments, the structure and material of impeller disc 124
may be
configured to function as a gyroscope. In some embodiments, the number, size
and shape of
blades 140 on impeller disc 124 may be configured to allow impeller disc 124
to function as a
gyroscope even when rotating at low rotational speeds. In some embodiments,
the structure
and material of impeller disc 124 including the number, size and shape of
blades 140 on
impeller disc 124 may be configured to allow impeller disc 124 to function as
a gyroscope
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when impeller disc 124 is rotating at speeds less than 50 revolutions per
minute. In other
embodiments, the structure and material of impeller disc 124 including the
number, size and
shape of blades 140 on impeller disc 124 may be configured to allow impeller
disc 124 to
function as a gyroscope when impeller disc 124 is rotating at speeds less than
30, 20 or 10
revolutions per minute.
[0035] Plenum chamber 128 is configured to retain impeller disc 124 and
provide water flow
between water intake 122 and control gates 132, wherein rotation of impeller
disc 124 in
plenum chamber causes water flow from water intake 122 through plenum chamber
128 to
control gates 132. In some embodiments, plenum chamber 128 comprises lower
wall 142
formed with opening 131 in fluid communication with water intake 122. As
depicted in
FIGURE 1, in some embodiments, plenum chamber 128 comprises bottom wall 129,
lower
wall 142 and upper wall. Lower wall extends from bottom wall 129 at a first
diameter
radially inward of water intake 122 to a second diameter radially outward of
outer edge 138
of impeller disc 124 and has openings 131 corresponding to water intake 122.
As impeller
disc 124 rotates, water is drawn in from water intake 122 through openings 131
and blades
140 accelerate the water in plenum chamber 128, wherein plenum chamber 128
directs the
flow of water through hull 110 to control gates 132. In some embodiments,
plenum chamber
128 is formed with upper wall 144 having a diameter larger than a diameter of
outer edge 138
of impeller disc 124, wherein water pushed radially outward by impeller disc
124 is
circulated around plenum chamber 128 to the plurality of control gates 132.
[0036] The design of plenum chamber 128 may contribute to one or more of a
buoyancy
associated with propulsion system 120, an increased operating efficiency of
propulsion
system 120, a reduction of acoustic noise emitted by propulsion system 120 and
the safety of
marine life that may inadvertently pass through propulsion system 120.
[0037] Plenum chamber 128 may be formed as a sealed chamber such that water
can flow
only through openings 131 and water intake 122 or any open control gates 132.
When all
control gates 132 are closed, air may be contained within plenum chamber 128
to provide
additional buoyancy. In some embodiments, the shape of plenum chamber 128 may
contribute to the buoyancy of hull 110. In some embodiments, plenum chamber
128
comprises upper wall 144, bottom wall 129 and lower wall 142 formed to
accommodate a
shape of impeller disc 124 and allow for additional air in plenum chamber 128
above or
radially outward if impeller disc 124. In this configuration, plenum chamber
128 allows a
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greater volume of air at a higher level and distributed over a wider area,
which contributes to
the buoyancy and the stability of hull 110.
[0038] Positioning impeller disc 124 in plenum chamber 128 may prevent
acoustic noise
generated by blades 140 from being directly emitted into the ambient water.
Lower wall 142
may be formed with a shape and surface to facilitate impeller disc 124 moving
water upwards
and accelerating the water radially outwards. In some embodiments, lower wall
142 may be
configured to reduce the amount of acoustic noise allowed to exit propulsion
system 120
directly into ambient water. For example, lower wall 142 may be configured to
deflect
acoustic noise away from water intake 122. In some embodiments, lower wall 142
may be
formed from a material or coated with a material to deflect or absorb acoustic
noise.
[0039] Lower wall 142 of plenum chamber 128 and angled surface 136 of impeller
disc 124
may be separated by a distance based on a desired volumetric flow of water
through
propulsion system 120. In some embodiments, lower wall 142 and angled surface
136 may
be separated by a minimum distance determined to minimize the risk of harming
marine life
that may inadvertently enter water intake 122 and pass through propulsion
system 120. In
some embodiments, lower wall 142 of plenum chamber 128 comprises a shape
complementary to the shape of angled surface 136 of impeller disc 124, wherein
a separation
distance between lower wall 142 and angled surface 136 is substantially
constant at all radii.
In other embodiments, lower wall 142 of plenum chamber 128 and angled surface
136 of
impeller disc 124 are shaped such that a separation distance decreases
radially outward.
[0040] As impeller disc 124 rotates in plenum chamber 128, blades 140 push
water upward
and accelerate the water radially outward, increasing the momentum of the
water. Once
water is raised in plenum chamber 128, plenum chamber 128 directs the water
toward the
plurality of control gates 132 arranged around the periphery of hull 110.
USE OF CONTROL GATES TO GENERATE THRUST
Control system 150 may open or close one or more control gates 132 to generate
thrust to
propel and steer marine vessel 100. Referring to FIGURES 1 and 3, one or more
control
gates 132 may be opened or closed by electric motors or a hydraulic system to
direct water
exiting the control gate 132 at an angle in a range 133 of angles. In some
embodiments, each
control gate 132 may be configured to rotate about a local vertical axis over
range 133 of
angles. In some embodiments, range 133 may be ninety degrees, wherein control
gates 132
may be opened to direct water exiting the control gate 132 at any angle within
range 133 of
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ninety degrees. Control gates 132 configurable to direct water flow at an
angle in a range 133
of angles may allow for fewer control gates 132 but increased options for
maneuvering
marine vessel 100 in a body of water. For example, control system 150 may open
or close
only one control gate 132 and rotate control gate 132 to steer marine vessel
100 or may open
or close a plurality of control gates 132 collectively but rotate individual
control gates 132 to
steer marine vessel 100. Control system 150 may open or close one or more
control gates
132 at one or more angles to propel and steer marine vessel 100 or may operate
a plurality of
control gates 132 collectively to propel marine vessel 100 in a forward
direction, an aft
direction, a port direction or a starboard direction, to turn the marine
vessel 100 toward port
or starboard, to rotate marine vessel about a point or to stop marine vessel
100. As depicted
in FIGURE 1, at least one control gate 132 located near the periphery of hull
110 at the stern
end of marine vessel 100 is open and at least one control gate 132 located
near the periphery
of hull 110 at the bow end of marine vessel 100 is closed. Water flow that is
directed out of
the at least one stern control gate 132 generates thrust. As a reaction,
marine vessel 100 may
be propelled in the opposite direction. Referring to FIGURE 3, for example,
control gates
132-1 and 132-4 may be open and control gates 132-2 and 132-3 may be closed
such that
thrust is generated in an aft direction to propel marine vessel 100 in a
forward direction. In
some embodiments, each control gate 132 comprises an outer surface that
reduces drag on
hull 110 when control gate 132 is closed.
[0041] In these configurations, controlling a direction of travel of marine
vessel 100 does not
rely on drag forces applied to a rudder. Instead, controlling a direction of
travel may involve
control system 140 opening a first set of control gates 132 and closing a
second set of control
gates 132. In these configurations, embodiments avoid inefficiencies such as
directional
propellers imparting drag on marine vessel 100.
MULTIPLE IMPELLER DISCS
[0042] In some environments or marine vessel applications, a hull 110 may be
configured
such that a single impeller disc 124 may provide insufficient increase in
water momentum for
marine vessel 100. For example, hull 110 may be formed with a large length to
width ratio
such that the diameter of impeller disc 124 is limited. Referring to FIGURE 4,
in some
embodiments, a marine vessel 400 may operate with two impeller discs 124 in a
single
plenum chamber 128. In some embodiments (not shown) multiple impeller discs
124 may be
positioned relative to a common water intake in hull 110. The water intake may
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elongated, such as an oval or rectangular design. In other embodiments (not
shown) each
impeller disc 124 may be positioned relative to a respective water intake such
as water intake
122 and each water intake 122 may be in fluid communication with plenum
chamber 128.
Multiple impeller discs 124 may counterrotate as depicted in FIGURE 4 or may
rotate in the
.. same angular direction.
[0043] The above disclosed subject matter is to be considered illustrative,
and not restrictive,
and the appended claims are intended to cover all such modifications,
enhancements, and
other embodiments which fall within the true spirit and scope of the
disclosure. Thus, to the
maximum extent allowed by law, the scope of the disclosure is to be determined
by the
broadest permissible interpretation of the following claims and their
equivalents, and shall
not be restricted or limited by the foregoing detailed description.
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