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. [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 EMBODIMENIYS)

[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. [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. [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 stem. 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 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 stem 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 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. [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 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 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 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 stem 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 stem 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 be 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.