Ships – Submersible device – Having propulsion unit
Reexamination Certificate
2002-06-12
2004-04-27
Sotelo, Jesus D. (Department: 3617)
Ships
Submersible device
Having propulsion unit
C114S151000, C440S038000, C440S047000
Reexamination Certificate
active
06725797
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to aquatic propulsion systems and more specifically to a generally submerged propulsion system for a surface ship.
2. Problems In The Art
Underwater vehicles, such as submarines, are currently pushed through the water using propeller-based propulsion system typically located at the stern of the vehicle. Drag forces acting on the vehicle cause the water in front of, and around the vehicle, to become displaced and turbulent in nature. These drag forces lead to decreased efficiency and a lower overall thrust. Further, such propeller-based propulsion systems cause an increase in the submarine's noise with an associated increase in speed. This may aid others in detecting the submarine, enabling its destruction.
The increase in noise is due largely to cavitation. Cavitation is the formation of water vapor bubbles caused by rapid propeller movement that creates a vacuum-like area in the incompressible water. The vapor pressure of the water forms a bubble. Surrounding water pressure soon violently collapses the bubble creating substantial noise.
As the speed of the submarine increases, a geometrically increasing wave generated by frontal water resistance limits the increase in speed and contributes to increased cavitation. This wave is the main resistance to high speed travel in surface vessels and plays a role in submarine speed, albeit less when the submarine is at a depth of greater than three submarine diameters below the surface.
In addition, as submarine speed increases, surface friction from turbulence-related viscous shear stress creates a boundary layer of retarded fluid along the surface of the moving vessel. In this boundary layer, eddies of high-speed fluid contact the surface, causing deceleration, sapping the watercraft's momentum. This boundary layer turbulence increases in magnitude as flow progresses rearward from the bow. Thus nearly all of the vehicle's surface boundary layer is turbulent. The friction or drag of a turbulent boundary layer is seven to ten times that of a laminar boundary layer, so the possibility of achieving significant reductions in vehicle drag by boundary layer management is attractive.
There have been attempts to reduce boundary layer friction on submarines. For example, in U.S. Pat. No. 4,346,662 to Rogers, a twin hull design incorporates extensive slots in the outer hull. These are kept open by a back-flush pump in the bow at low speed. At high speeds, the bow pump is inactivated while the main pump at the stern exhausts water that has been pulled through the slots by suction. This is the sub's main propulsion. However, high Reynolds numbers (friction) limited practical application.
U.S. Pat. No. 3,779,199 to Mayer also discusses boundary layer control. Mayer did not solve the boundary layer problem beyond the bow, where the problem mainly exists. The Mayer patent eliminated the conventional propeller and rudder. However, such an arrangement loses efficiency due to poor management of the slipwater at the stern. The small intake diameter at the bow end did not approach the submarine diameter. The water exited through a large number of exit ports behind the intake in the bow region. The large numbers of parallel bow exit slots were arranged in a number of concentric rings. These were used for directional flow and as the only source of propulsion. Due to aforementioned reasons, the Mayer patent was not utilized in a practical submarine application.
Short of eliminating surface resistance and wave generation by other means, stealth submarine speed is slow, and top speed is below that of important surface ships, such as an aircraft carrier. Submarine surfaces are presently coated with rubber to make it less reflective to sonar and mute submarine noise. Stealth is the priority with submarines, it has always been the priority.
Surface water vehicles typically rely on a propeller fan, either by an inboard or outboard stern positioned engine, for propulsion. This application of power to the rear end creates an inverted pendulum, with stability problems. Further, a stern drive arrangement requires the vehicle to be pushed through the water, causing geometrically disproportionate wave drag with any increase in speed. This wave arises from displacing all the water in front of the vehicle, to areas around and behind the vehicle, limiting stability, efficiency and speed. Currently, improved water jet engines are placed at the stem of craft that exhaust the water jet outward, above the waterline. However, they are still subject to the preceding limitations of stem-drive only. They are a variation of the original water-jet engine that accelerates water through a curved passageway. Attempts have been made to address these problems for surface water vehicles. For example, U.S. Pat. No. 5,634,419 to Cymara discloses what is called a “front-drive boat” wherein a propeller propulsion system is located towards the front (bow) of the boat, which is claimed to increase stability of the boat. It corrects the problem of power to an inverted pendulum.
Further, U.S. Pat. No. 4,680,017 to Eller, entitled “Motorboat Propeller Guard For Improved Performance”, places a propeller inside a housing with grids configured to attempt to direct propelled water rearward for improved performance (higher speed). It is a jet-like stem drive system. Similar designs, including the stem pumpjet used on modem stealth submarines, follow earlier torpedo pumpjet designs. Cavitation (generation of noisy water vapor bubbles) was reduced in the pumpjet through pressurizing the propeller blade areas and eliminating the propeller tip vortices, making higher speeds at stealth possible. Herein incorporated by reference, U.S. Pat. Nos. 5,383,801 to Chas, U.S. Pat. No. 4,902,254 to Chas, and U.S. Pat. No. 4,831,297 to Taylor et al., disclose propulsion systems for over the water craft that adopt jet engine principles to attempt to increase propulsion. Another propeller based propulsion system is U.S. Pat. No. 5,252,875 to Veronesi, et al, herein incorporated by reference.
Many of the above patents resemble a jet engine in appearance and further resemble a jet engine in the manner in which they are attached to a vehicle; i.e. they hang down from the craft. However, they still have to push a boat through the water, causing wave displacement that increases geometrically with speed, none have twin jet accelerators in sequence and none of the above referenced patents are capable of supercavitation. Currently, only munitions, including rocket powered blunt-nosed torpedoes and high-velocity blunt nosed supercavitating bullets, are capable of any sustained supercavitation. However, the rocket or explosive style propulsion systems have limited range and would be very dangerous for use in passenger travel. There is another patent that deals with decreasing drag to improve stealth and speed. It involves two or more propulsion units in sequence (stages)to power a submarine. A preferred embodiment discusses a two-stage bow propulsion system combined with a conventional stem propeller. The bow stage one vanes and stage two vanes can be selectively employed, individually, or in combination. The two bow stages allow a choice between supercavitation (very fast and noisy), or higher speed stealth (faster silent running) propulsion.
Engaging both twin bow stages on the jet-drive submarine and/or torpedo in U.S. Pat. No. 6,427,618 B1 by Hilleman offers a supercavitating generation platform. Water is incompressible; it is a high-pressure to high-velocity device. The first bow stage minimizes cavitation while it propels the submarine through the water and feeds the second stage. The bow second-stage propeller's high velocity, combined with the enclosing shroud, the shroud's trailing edge, high-speed lower-pressure nozzle emission, and water vapor pressure, can create a large long vapor cavity (supercavity). The radial velocity of the tangential-to-flow movement of the stage two vanes can easily achieve speeds
McKee Voorhees & Sease, P.L.C.
Sotelo Jesus D.
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