US 7299763 B2
A boat hull has at least one ventilating propulsion tunnel formed therein open to the water forward of the hull's transom and adapted to contain a propeller of the propulsion system. The tunnel has a leading edge forward of the transom and an interceptor plate projects downwardly from the hull at the leading edge.
1. A boat or ship hull having at least one ventilating propulsion tunnel formed therein open to the water; said tunnel having a leading edge forward of the hull's transom defining a cutwater whereby the water surface beneath the tunnel lies at the level of the tunnel leading edge and remains generally flat beneath the tunnel, said tunnel being adapted to contain a propeller of the propulsion system, and said hull including interceptor plate means for linear reciprocal movement relative to the adjacent surface of the hull whereby the interceptor plate means may be selectively extended from and retracted relative to the hull.
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3. A boat or ship hull having at least one ventilating propulsion tunnel formed therein open to the water; said tunnel having a leading edge forward of the hull's transom and being adapted to contain a propeller of the propulsion system, said hull including an interceptor plate projecting therefrom at said leading edge downwardly from the hull; and side plates projecting from said hull located at the propulsion tunnel leading edge corners and running forward therefrom; said side plates projecting from said hull approximately 2 to 4 inches at the propulsion tunnel leading edge and tapering forwardly to a height of approximately zero.
4. A hull as defined in
5. A watercraft vessel comprising a hull having at least one ventilated propulsion tunnel formed therein opening downwardly to the water surface when the hull is on the water, said tunnel having a leading edge located rearwardly of the LCG of the vessel defining a cutwater whereby the water surface beneath the tunnel lies at the level of the tunnel leading edge and remains generally flat beneath the tunnel; a surface operating propeller partially enclosed in the tunnel for partial immersion in the water, and an interceptor plate mounted on said hull at the leading edge of the tunnel for linear reciprocal movement relative to the adjacent surface of the hull to project a predetermined distance downwardly from the hull.
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7. A watercraft vessel comprising a hull having at least one ventilated propulsion tunnel formed therein opening downwardly to the water surface when the hull is on the water, said tunnel having a leading edge located rearwardly of the LCG of the vessel; a surface operating propeller partially enclosed in the tunnel for partial immersion in the water, and an interceptor plate mounted on said tunnel at the leading edge of the tunnel to project a predetermined distance downwardly from the hull; said hull containing two ventilated propulsion tunnels and two movably mounted interceptor plates respectively located adjacent the leading edges of said tunnels.
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11. A watercraft vessel comprising a hull having at least one ventilated propulsion tunnel formed therein opening downwardly to the water surface when the hull is on the water, said tunnel having a leading edge located rearwardly of the LCG of the vessel; a surface operating propeller partially enclosed in the tunnel for partial immersion in the water, and an interceptor plate mounted on said tunnel at the leading edge of the tunnel to project a predetermined distance downwardly from the hull; and a pair of side plates extending from said hull from positions adjacent the leading edge corners of the tunnel forward a predetermined distance, said side plates being triangular with one leg adjacent the interceptor plate and tapering from that legforwardly to a point.
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This application claims the benefit of U.S. Provisional Application No. 60/637,736, filed Dec. 22, 2004.
The present invention relates to boat hulls and more in particular to boat hulls having ventilating propulsion tunnels containing surface propellers.
Watercraft speed efficiency is achieved by reducing craft drag and improving the efficiency of the propulsion system. The result is higher speeds for the same amount of power used or less power needed to achieve the same speed.
Two prior art technologies previously developed to accomplish these goals are surface propellers operating in ventilating propulsion tunnels formed in the watercraft hull and flow interceptors attached to the transom of a watercraft. Flow interceptors project downwardly from the transom below the hull surface either vertically or at an angle. One such system is shown in U.S. Pat. No. 6,006,689.
It has been found that the use of surface propellers in ventilating propulsion tunnels improves the control of water flow to the propeller and thereby improves propulsive efficiency. The use of propulsion tunnels in this way also reduces the hull and appendage wetted area, thereby reducing drag. In addition, on the other hand, propulsion tunnels reduce the amount of the buoyant and dynamic lift of the hull.
Transom mounted flow interceptors have been found to reduce hull drag by providing lift which reduces hull immersion in the water. Reducing hull drag improves watercraft seakeeping and propulsive efficiency by providing trim control forces to achieve the optimal watercraft trim (which varies with speed), watercraft weight and sea conditions. Such systems are usually mounted directly at the transom, which creates large trimming moments that can push the bow down and create an adverse trim condition.
It is an object of the present invention to increase dynamic lift in hulls having ventilating propulsion tunnels.
It is a further object of the invention to reduce wetted surface area and drag in hulls having ventilating propulsion tunnels.
Yet another object of the invention is to provide dynamic lift to a hull replacing buoyant lift lost by the presence of ventilating tunnels, while minimizing trimming moments on the hull.
In accordance with an aspect of the present invention a flow interceptor is provided at the leading edge of a boat hull's ventilating propulsion tunnel to improve control of the water flow and propulsive efficiency. The leading edge propulsion tunnel interceptor (LEPTI) of the invention reduces wetted area and drag and provides dynamic lift more efficiently than the buoyant lift amounts lost by the presence of a tunnel or tunnels.
As compared to a transom mounted interceptor, the LEPTI provides greater lift and reduction of hull immersion and also provides comparable trim control forces.
In conventional ventilating propulsion tunnel hulls, the depth of water flow to the propeller in the ventilating propulsion tunnels is the depth of the tunnel cutwater, i.e., the depth of the front edge of the tunnel. LEPTI provides a means of deepening the flow coming off a simple cutwater to the depth of the immersed interceptor. It thereby reduces propeller and propeller appendage drag by reducing the height of the flow aft of the interceptor and increasing the unwetted area of the rudder, propeller, propeller hub, shaft and strut.
By producing more hull lift with the interceptor a greater reduction in hull immersion and therefore drag is produced. By using LEPTI, a greater amount of lift also can be generated on the hull as compared to that created by prior art transom mounted interceptors. Moreover, since the LEPTI is closer to the longitudinal center of gravity (LCG) of the hull, the lift it generates will create a lower trimming moment than the same amount of lift generated by a transom mounted interceptor, which is further from the LCG. Trimming moments will eventually push the bow down to an excessive and adverse bow down trim condition and the onset of this condition will be reached later with the greater lifting force and lesser trimming moment provided by the LEPTI.
The use of the LEPTI in accordance with the invention produces more consistent flow to the propellers and therefore higher efficiency than prior art prop tunnels with simple cutwaters. The velocity of flow coming off a conventional propulsion tunnel cutwater can vary in direction and speed because of hull surface variations causing drag and flow direction variations. Velocity of the flow coming off an interceptor is more consistent in direction and speed since the stagnation line in front of the interceptor reduces the flow velocity across that line to 0 and then consistently accelerates the flow behind the interceptor to a consistent speed and flow direction.
The above and other objects, features and advantages of the present invention will become apparent from the following detailed description thereof, which is to be read in conjunction with the accompanying drawings, wherein:
Referring now to the drawings in detail, and initially to
In accordance with the present invention, immediately forward of the propulsion tunnel 14, an interceptor plate 24 is provided at the leading edge of the tunnel which depends downwardly from the surface of the bottom 20 of the hull 10. Immediately forward of interceptor plate 24 are a pair of spaced generally triangular side plates 26 which are either fixed to the hull or integrally formed with the interceptor plate 24.
The construction of the interceptor plate is more clearly illustrated in
In conventional ventilating propulsion tunnel hulls, the leading edge of the tunnel 28 forms a so-called “cutwater” so that the water surface beneath the tunnel generally lies at the level of that tunnel leading edge and remains generally flat beneath the tunnel so that the part of the tunnel above the water surface contains air while the propeller is only partially immersed in the water. As noted above, this arrangement reduces drag on the vessel by eliminating substantial immersion of the shaft and propeller.
In accordance with the present invention, the leading edge propulsion tunnel interceptor (LEPTI) consisting of the interceptor plate 24 and the side plates 26 (only one of which is seen in the side view of
The leading edge propulsion tunnel interceptor may also be referred to as a spoiler or a vertical trim tab. It is either fixed in place or movably mounted on the hull.
Preferably, as described hereinafter, the position of at least the vertical interceptor plate 24 is adjustable so that the amount of penetration of the interceptor plate into the water beneath the hull may be varied. The provision of an LEPTI in accordance with the invention creates an adjustable cutwater that allows the operator to control the height of the free surface immersion of the surface propeller within the tunnel, thereby reducing drag as described above, and reducing propeller loading. The practical range of adjustment is small, for example, perhaps up to 3 inches, but at low speeds there is a synergistic effect provided by the LEPTI between the benefit of reducing propeller loading and the resistance created when engine rpm and torque is low.
The LEPTI of the invention also effectively functions as a lift augmentation appendage by creating a high stagnation pressure on the hull immediately forward of the interceptor. This also reduces drag by reducing the total area of hull immersed in the water.
The function of the side plates 26 on the hull is to contain the stagnation pressure and to mitigate tip vortices in the ventilating propeller tunnel and also to prevent separated flow of the trailing edge of the interceptor, which would occur if the tunnel was not ventilated.
In addition, because the propeller tunnel is forward of the transom 12, its leading edge is thereby closer to the longitudinal center of gravity of the hull (the LCG) than the transom. Thus, the lift generated at the hull immediately forward of the interceptor has a lower pitching moment than if the lift is generated at the transom, as occurred with conventional interceptors. This creates the further benefit of allowing greater lift to be generated without adversely effecting vessel trim.
Another embodiment of the invention is illustrated in
In another embodiment of the invention, each of the interceptor plates 24 may be segmented and connected to separate controls so that the amount of liquid intercepted and the pattern of flow and the trim adjustment caused by the interceptors may be varied.
It is noted that in the illustrative embodiment of the invention the interceptors 24 are shown as extending only along the width of the ventilating tunnel. However, it is contemplated that these plates may be wider than the ventilatiing tunnels themselves and extend, for example, from a position near the keel 30 to the chine 22 on the sides of the vessel, across the front of the tunnel.
Applicant has conducted computer based studies with respect to boat hulls having ventilated propulsion tunnels and interceptor plates according to the present invention in order to confirm their effectiveness. The displacement/length ratio of one boat hull studied in connection with this invention was projected to be approximately 250. That ratio is higher than the corresponding ratio for standard planing hulls (which is approximately 220), and indicates that the particular hull studied is “overloaded” and could utilize aid from an auxiliary lifting device. To investigate its effectiveness, an interceptor plate was located across the entire leading edge of the power vent tunnels on the hull which was modeled. As noted before, the leading edge of the prop tunnels is closer to the LCG of the vessel so that placing interceptors at that location decreases the pitch moment from the vessel. In addition, the width of the prop tunnels provide a more effective area for the interceptors than the small space generally available between the tunnels at the transom where such interceptors have been placed in the past.
Because placing the interceptors at the leading edge of the tunnel could have an adverse effect on the flow of water in the tunnel, for example by vortex generation, the side plates 26 were included in the model to mitigate vortex generation and maximize interceptor efficiency. As noted above, the interceptor and side plates may be fixed to the hulls or molded together for simultaneous operation. They also could be independently mounted for independent operation and retraction into and out of the hull, using either the electro-mechanical or hydraulic structures previously described.
The computer studies of this hull form were conducted using a known CFX software with the hull at a trim of 5° over a speed range of 20-35 knots. That matched the bare hull's 16 lt (long tons) draft for all speeds.
Based on this, it is seen that both the ˝″ and 1″ interceptors provide an increase in total lift at every studied speed, except that the lift at 20 knots was minimal. This would suggest that the interceptors be deployed to extend from the vessel at speeds above 20 knots. At the highest speed studied, the 1″ interceptor deflector plate provided eight long tons more lift than the bare hull at the same speed, thereby demonstrating the effectiveness of the system.
The computer studies have also demonstrated that there is a significant change in the water surface profile within the prop tunnel with the interceptor plates extended. As seen in
The effect on the water surface conditions at the ventilating propulsion tunnels is significant because it reveals that an adjustable interceptor located at the leading edge of the prop tunnel could be used as a method to control the water surface level at the prop, i.e., to control prop immersion. This would be a tremendous aid in broadening the effective speed range of the propellers. An additional computer analysis of the streamlines and vectors of water flow past the interceptor plate did not expose any significant vortices or cross flows in the tunnel. This indicates that the interceptors do not disrupt the flows to the propellers.
In addition, as the interceptors lift the hull out of the water, the hull becomes more efficient. As seen in
Although illustrative embodiments of the present invention have been described herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to these precise embodiments and that various changes and modifications may be effected therein without departing from the scope or spirit of this invention.