SURFACE EFFECT HULL CONFIGURATION UTILIZING REBOUND HUMP SEAL

Abstract

A boat hull configuration for a boat includes a hull body having an air cavity created on an underside thereof that receives pressurized air from a blower through a blower inlet or plenum. The plenum is positioned in the cavity such that it divides the air cavity into a bow portion and an aft portion. The upper surface of the bow portion of the air cavity is configured to form a seal with a rebound hump produced by the hull body moving across a water surface when the ship is operating in a given speed range. This seal prevents air from venting from the forward portion of the air cavity when the bow of the hull rises during start up. The upper surface of the aft portion of the air cavity is positioned such that it does not come into contact with the rebound hump as the hump moves toward the aft of the hull as the boat accelerates. At high speeds, the rebound hump is behind the boat and the entire air cavity is pressurized and providing the maximum amount of lift and drag reduction.

Description

CROSS-REFERENCES TO RELATED APPLICATIONS

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STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

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REFERENCE TO SEQUENCE LISTING OR COMPUTER PROGRAM LISTING APPENDIX

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FIELD OF THE INVENTION

The present invention is directed toward a boat hull configuration for a vessel having air filled cavities. More particularly, the present invention is directed toward a boat hull having an air cavity shaped to utilize a rebound hump as a seal with a determinable speed range.

BACKGROUND OF THE INVENTION

Surface effect vessels which use cushions of air to provide lift and reduce friction between the boat's hull and the water are well known in the prior art. Basically, surface effect vessel technology involves injecting pressurized air under or between the hulls of a boat so that at least a portion of the boat's hull rides upon a cushion of air. By utilizing gas pressure contained within a pocket under the hull, a surface effect vessel can operate at higher speeds and reduced power levels as compared to conventional vessels. This increased performance is due to the fact that the friction between the air cushion and the boat hull is substantially less than the friction between the water and the boat hull. Thus, riding upon a cushion of air allows a surface effect vessel to reach higher speeds and operate more efficiently with a smaller engine than a typical vessel.

There are many prior art designs which utilize this surface effect. One of the primary problems with these prior art designs is that the water/air seal allows excessive amounts of air to escape. This air loss increases the volume and pressure of the air required to maintain an air cushion under the vessel. Producing and providing pressurized air requires power from the vessel's engines and blowers. Thus, the efficiency and performance of the vessel are greatly diminished when air escapes from the supporting air cushion. In addition, venting of the air substantially increases the drag of the hull and causes the vessel to lurch.

Prior art surface effect vessels suffer from particularly excessive venting and increased and variable drag during startup. This is due to the fact that a certain amount of speed is required for the boat to reach a planning equilibrium and establish consistent seals around the air cushions. During startup, the bow raises causing air to vent from the front of the air cushion. If the air cushion is only positioned toward the aft of the vehicle, the bow is not supported at high speeds. Thus, when starting out, prior art vessels often seem lethargic even though they may ultimately reach very high top speeds.

A familiar effect from a ship planing on the surface of the water is the wake rebound hump created in the water behind the vessel. The rebound hump is caused by the weight of the boat forcing down the water under the hull as the boat passes over. The displaced water then rebounds forming a hump behind the vessel. The distance between the back of the boat and the rebound hump, and the size and shape of the rebound hump, primarily depend upon the depth of immersion of the hull, the shape, and in particular the width, of the boat hull and the speed at which it is moving over the water's surface. Prior art surface effect vessels have a problem in that, at low speeds, the rebound hump may contact the inner surfaces of the air cushions and cause excessive drag. To prevent this, most prior art vessels increased the height of the air cavities to minimize contact between the rebound hump and the air cavities hull surface at low speeds. Placing the blower at the front of the air cavities tended to depress the rebound hump but resulted in the air cavity venting when the bow rises during startup. Therefore, in light of the above discussed problems with the prior art, what is needed in an improved air cushion hull configuration.

SUMMARY OF THE INVENTION

A boat hull configuration for a boat includes a hull body having a multi-hull configuration with two or more side hulls wherein each side hull has a supporting air cavity created on an underside thereof that receives pressurized gas/air from a source such as a blower through a set of air ducts that lead to a plenum or air outlet in the air cavity. The plenum is positioned in a central location in the air cavity such that a portion of the air cavity is in a bow location with respect to the plenum and a portion Of the air cavity is in an aft location with respect to the plenum. The plenum preferably introduces the pressurized air into the air cavity with an aftward flow direction. An upper surface of the air cavity is configured to form a seal with a rebound hump produced by the hull body moving across the waters surface. The upper surface of the air cavity in the bow portion is closer to the water surface than an upper surface of the aft portion of the air cavity when the hull is substantially motionless with respect to the water's surface. The upper surface of the aft portion of the air cavity is positioned such that it does not come into substantial contact with the rebound hump when the pressurized hull body is moving with respect to the water's surface. As a result, the aft portion of the air cavity contains pressurized air and the bow portion of the cavity contains water when the boat hull is moving below a determinable speed.

Another embodiment of the present invention is directed toward a surface effect ship that includes a pressurized air cavity. The air cavity is dimensioned to utilize a rebound hump created by a hull of the surface effect ship moving over the water's surface to prevent venting of air from the air cavity when the surface effect ship is traveling within a specified speed range. An upper surface of a portion of the air cavity does not come into contact with the rebound hump when the surface effect ship is moving with respect to the water's surface. The air cavity is also constructed such that a first portion of the air cavity contains air and a second portion of the cavity contains water when the surface effect ship is moving below a certain speed with respect to the water's surface. An exhaust gas entrance introduces exhaust gas from an exhaust trunk coupled to the surface effect ships engines into the air cavity to provide additional lift and establish an aft pressurized gas pocket area.

Yet another embodiment of the present invention is directed toward a method of preventing air from venting from a supportive air cavity of a ship that has a plenum for introducing pressurized air into the supportive air cavity. In accordance with the method, a rebound hump created by a portion of a hull is used to prevent air from venting from the air cavity when the ship is traveling below an approximate speed. Pressurized air is introduced into the air cavity with an aftward flow direction to further prevent forward venting. A portion of the air cavity in front of the plenum is positioned to maintain a degree of contact with the water when a portion of the air cavity behind the plenum is supported by the pressurized air when the ship is moving within a desired speed range.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a boat hull constructed in accordance with a first embodiment of the present invention;

FIGS. 2(a-d) are exemplary illustrations of a prior art surface effect hull constructed in accordance with an embodiment of the present invention in a still, low speed, medium speed and high speed condition with respect to a liquid water surface;

FIGS. 3(a-d) are exemplary illustrations of a hull constructed in accordance with an embodiment of the present invention in a still, starting, slow speed, medium speed and high speed condition with respect to a liquid water surface;

FIG. 4 is an illustration of an exhaust gas inlet for injecting exhaust gas into the air cavity of a surface effect ship constructed in accordance with an embodiment of the present invention; and

FIG. 5 is a flow chart of a process for designing a hull in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, an illustration of a boat hull 2 constructed in accordance with a first embodiment of the present invention is shown. The boat hull 2 consists of two or more side hulls 4 and 6 in a multi-hull configuration. Each side hull 4 and 6 has a respective air cavity 8 and 10. An air inlet or plenum 12 and 14 is provided in an approximately central location of each air cavity 8 and 10. Air is pushed through the plenums 12 and 14 into the air cavities 8 and 10 to lift the hull 2 and decrease the drag of the hull when the hull is moving over the water's surface. The front portion 16 of each cavity is raised with respect to the adjacent bow hull 18. However, the front portions 16 of the air cavities 8 and 10 are slightly lower than the back portions 20 of the air cavities. The front portions 16 are positioned with respect to the adjacent bow hull 18 such that the rebound hump of the bow hull contacts the front portions 16 of the air cavities 8 and 10 when the boat is starting up or moving slow. The contact between the rebound hump created by the bow of the hull 2 and the front portions 16 prevents air from the plenums 12 and 14 escaping through the front portions 16 of the air cavities when the boat is moving at these slow speeds. This ensures that the back portions 20 of the air cavities 8 and 10 are filled with pressurized air at these slow speeds. However, when the boat speeds up the rebound hump separates from the front portions 16 of the air cavities 8 and 10 and moves toward the rear of the vessel, opening up a path for air to flow from the plenums 12 and 14 to the front portions 16 of the air cavities. This allows the entire air cavity to support the vessel when the vessel reaches high speeds so that the maximum possible top speed of the vessel is achieved.

Water directing projections 9 are placed forward of the leading edge of the air cavities 8 and 10. The water directing projections 9 produce a high velocity column of water that is directed toward the edges Of the air cavities 8 and 10. The high velocity water flow from the water directing projections 9 minimize venting of pressurized air from the edges of the air cavities 8 and 10.

Preferably, the blowers for the air cavities 8 and 10 are independently adjustable. Providing independently adjustable air pressures allows an operator, or automated control system, of the vessel to compensate for any tendency for the vessel to lean to one side or the other due to any one of a variety of conditions such as turning or unbalanced loading.

To better understand the benefits of the present invention, it is necessary to fully understand the problems associated with an air cushion operation. Referring now to FIGS. 2(a-d), a hull 30 utilizing an air cavity 34 is shown. The examples of FIGS. 2(a-d) are discussed with respect to the performance of a typical 40′ to 80′ vessel, but are exemplary only and the performance of any vessel will depend upon its particular configuration. As shown in FIG. 2(a), in a resting condition without the blower activated, the air cavity 34 is full of water 36.

In FIG. 2(b), the blower outlet or plenum 32 is providing air to the cavity 34 and the hull 30 is moving forward at a slow speed. Although the actual speed at which the condition of FIG. 2(b) occurs will depend upon the particular hull, an exemplary speed range would be less than 10 knots. To minimize slow speed drag, the plenum 32 has been placed near the center of the air cavity 34. As the hull's 30 speed with respect to the water 36 begins to increase, the hydrodynamic planning of the bow of the hull 30 lifts up the bow causing the air in the air cavity 34 to flow to the front of the air cavity 34. The rebound hump 38 substantially misses the top of the air cavity 34 and only briefly contacts the rear of the air cavity 34. Although the rebound hump 38 and the water's 36 contact with the rear of the hull 30 provides an amount of planning lift to the aft of the vessel, due to the relatively low speed of the hull 30, this planning lift is not enough to prevent the bow of the hull 30 from rising. As the hull's speed further increases, the bow rises further until the condition of FIG. 2(c) is likely to occur, particularly in rough water, wherein the front of the air cavity 34 vents and the air cavity partially collapses and fills with water 36 causing the hull's drag to increase dramatically and the hull to momentarily lurch and slow down. An exemplary speed range for the condition of FIG. 2(c) for a boat hull constructed in accordance with a preferred embodiment of the present invention is about 12-18 knots. However, at a high rate of speed, as shown in FIG. 2(d), a high amount of planning lift is finally created by the contact of the water with the aft of the hull 30. Thus, the aft of the hull 30 rises, forcing the bow down and sealing the front of the air cavity 34 against the water's 36 surface. Since the air cavity 34 is fully pressurized and providing full air cavity lift and drag reduction, the drag of the hull 30 is reduced and the full speed potential of the hull can be realized. The rebound hump 38 has now moved beyond back of the boat and is no longer influencing the air cavity 34. Such a condition can be expected at speeds exceeding 25 knots for a typical surface effect vessel.

A hull constructed in accordance with a preferred embodiment of the present invention overcomes the initial low speed venting and increased turbulence and drag problems associated with the hull of FIGS. 2(a-d) by dimensioning and positioning the upper surface of the front portion of an air cavity having a centrally located plenum or blower entrance to form a seal with the rebound hump at the initial starting speeds. Referring now to FIGS. 3(a-d) the operation of a hull 60 constructed in accordance with an embodiment of the present invention is illustrated. As illustrated in FIG. 3(a), when the hull 60 is at rest and the plenum 62 is not introducing pressurized air into the air cavity 64, the cavity 64 is primarily filled with water 67. At very slow speeds, as shown in FIG. 3(b), negligible amounts of planning lift are created by the bow and stern hull 60 portions. Due to the lowered upper surface of the front portion 66 of the air cavity 64 and the aft directed plenum 62, only the aft portion 68 of the air cavity 64 is filled with pressurized air from the plenum 62. By providing the entire air supply to the back portion 68 of the air cavity 64 during startup and slow operation, the stern of the hull 60 is supported which reduces bow rise. In addition, even if the bow of the hull 60 does rise during start up speeds, the air is primarily contained in the back portion 68 of the cavity 64 and venting is substantially reduced.

As the hull accelerates, the surface of the water 67 begins to separate from the upper surface of the air cavity 64 as shown in FIG. 3(c). However, a rebound hump 69 is now formed that contacts the lowered surface 63 of the front portion 66 of the air cavity 64. This rebound hump 69 forms a substantial seal along the upper surface 63 of the air cavity that prevents air from escaping from the rear 68 of the air cavity 64 during slow to medium speed operation. However, as shown in FIG. 3(d), at high speeds the rebound hump 69 extends beyond the aft most portion of the hull 60 which allows the entire air cavity 64 to be pressurized for full speed operation. The raised upper surface 65 of the back portion 68 is preferably positioned such that the rebound hump 69 does not form sealing contact with the surface 65 when the hump 69 moves through the back portion 68 of the air cavity.

Due to the complexity of fluid mathematics, the proper distance to raise the hull on the front edge of the air cavity such that the rebound hump forms a seal with the upper surface of the air cavity during a desired range is best determined experimentally using computer CFD simulations or towed tank models. The shaping of the hull in front of the air cavity can be used to aid in rebound hump formation. A steeper slope on the hull in front of the cavity will produce a rebound hump that is higher. Conversely, a hull slope substantially parallel to the waters surface will produce a smaller rebound hump that is closer at a similar speed. The weight of the vessel ultimately supported will also affect the size and position of the rebound hump and variations in loading of the vessel may need to be taken into account during the design process depending upon the vessel's ultimate function and desired performance.

To further increase the efficiency and speed of a vessel, exhaust gas is preferably introduced into the air cavity 71 of a hull 70 as illustrated in FIG. 4. An exhaust gas exit 72 is provided in the air cavity 71 that is sloped or deflected toward the aft of the hull 70 to minimize introduction of water into the exhaust gas exit 72 and to further facilitate an aft ward flow direction for the pressurized air or gas. This provides additional lift in the cavity 71 without placing substantial additional power demands on the vessel's engines. In addition, the proper positioning of the exhaust gas exit 72 in the air cavity 71 muffles the engine noise and disperses the exhaust gas in an inconspicuous manner.

Referring now to FIG. 5, a process for designing a hull in accordance with an embodiment of the present invention is shown. The process begins in step 80 with the selecting of a hull configuration for surface effect ship. Once a hull configuration is selected, the position and outer dimensions of a supporting air cavity on the underside of the hull are determined in step 81. The positioning size and shape of the air cavity are usually determined by the desired footprint of the hull in the water and performance of the vessel. Next, in step 82, a position for a plenum in the air cavity is selected. Tests are then performed to determine the height and shape of the rebound hump created by the hull in the front portion of the air cavity forward of the plenum in step 83. The upper surface of the front portion is then dimensioned, in step 84, to form a seal with the rebound hump at slow speeds that helps prevent pressurized air from escaping through the front portion of the air cavity. Tests are performed in step 85 to determine the height and shape of the rebound hump created by the hull in the portion of the air cavity aft of the plenum. Finally, the upper surface of the aft portion of the air cavity is dimensioned to allow the rebound hump to pass underneath the upper surface of the aft portion is step 86. By following the above described design process, any surface effect ship can be designed to utilize the rebound hump to seal the air cavity in accordance with the present invention.

Although there have been described particular embodiments of the present invention of a new and useful SURFACE EFFECT HULL CONFIGURATION UTILIZING REBOUND HUMP SEAL, it is not intended that such references be construed as limitations upon the scope of this invention except as set forth in the following claims.

Claims

1. A boat hull configuration for a boat, said boat hull configuration comprising:

a hull body having an air cavity created on an underside thereof for receiving pressurized air or gas from a blower through a plenum wherein said plenum is positioned in said cavity such that a portion of said air cavity is in a bow location with respect to said plenum and a portion of said air cavity is in an aft location with respect to said plenum and wherein an upper surface of said air cavity is configured to form a seal with a rebound hump produced by said hull body moving across a water surface.

2. The boat hull configuration of claim 1 wherein said hull body further comprises a multi-hull configuration with at least two hulls wherein each hull has a supporting air cavity.

3. The boat hull configuration of claim 1 wherein said plenum is positioned in a central location of said air cavity.

4. The boat hull configuration of claim 1 wherein said upper surface of said air cavity in said bow portion is closer to the water surface than an upper surface of said aft portion of said air cavity when said hull is substantially still with respect to said water's surface.

5. The boat hull configuration of claim 1 wherein said plenum introduces said pressurized air into said air cavity with an aftward flow direction.

6. The boat hull configuration of claim 1 wherein an upper surface of said aft portion of said air cavity is positioned such that it does not come into substantial contact with said rebound hump when said hull body is moving with respect to said water's surface.

7. The boat hull configuration of claim 1 wherein said air cavity is constructed such that said aft portion of said air cavity contains air and said bow portion of said cavity contains water when said boat hull is moving below a determinable speed.

8. A surface effect ship comprising:

a pressurized air cavity wherein said air cavity is dimensioned to utilize a rebound hump created by a hull of said surface effect ship moving over a water's surface to prevent venting of air from said air cavity when said surface effect ship is traveling in a speed range.

9. The surface effect ship of claim 8 wherein said air cavity is shaped such that a first portion of said air cavity contains air and a second portion of said cavity contains water when said surface, effect ship is moving below a certain speed with respect to said water's surface.

10. The surface effect ship of claim 8 wherein an upper surface of a portion of said air cavity does not come into contact with said rebound hump when said surface effect ship, is moving with respect to said water's surface.

11. The surface effect ship of claim 8 further comprising a plenum that introduces said pressurized air into said air cavity with an aftward flow direction.

12. The surface effect ship of claim 8 wherein an upper surface of said air cavity in a bow portion of said air cavity is closer to the water surface than an upper surface of an aft portion of said air cavity when said hull is substantially still with respect to said water's surface,

13. The surface effect ship of claim 8 wherein said hull further comprises a multi-hull configuration with at least two hulls wherein each hull has an air cavity.

14. A method of designing a supportive air cavity for a surface effect ship, said method comprising the steps of:

using a rebound hump created by a portion of a hull of said surface effect ship to prevent air from venting from said air cavity when said surface effect ship is traveling below an approximate speed.

15. The method of claim 14 further comprising the step of introducing pressurized air into said air cavity with an aftward flow direction.

16. The method of claim 14 wherein said surface effect ship further comprises multiple hulls.

17. The method of claim 14 wherein a front portion of said air cavity is in at least some contact with water when a back portion of said air cavity is supported by said pressurized air when said surface effect ship is moving in a speed range.

18. The method of claim 14 wherein a hull surface of a front portion of said air cavity is lowered with respect to a hull surface of a back portion of said air cavity.

19. The method of claim 14 further comprising the step of introducing exhaust gas into said air cavity.

20. The method of claim 19 further comprising the step of introducing said exhaust into said air cavity with an aft ward flow direction.