Abstract:
A twin-hull catamaran boat or vessel comprising of four hydrodynamic pod sections connected with a mid-span recess on each hull that receives mechanically inducted gas or air for hull support. Each hull shape of the twin-hull catamaran configuration contains one V-shaped hull portion forward (bow), one mid-length hull cavity portion that receives pressurized gas or air therein (amidships), and one V-shaped hull portion aft (stern). The V-shaped bow portion creates hydrodynamic lift, the air or gas mechanically pressurized mid-length recess portion creates an air cushion to lift the hull in order to reduce wetted surface and drag on the hulls, and the V-shaped stern portion provides hydrodynamic lift to support the aft portion of the twin-hull catamaran configuration and also to provide an aft sealing body for the mechanically pressurized air or gas mid-length cavity. The benefit of the hull configuration as described herein results in lower resistance and uses less horsepower to attain a specific boat or vessel speed.

Description:
RELATED APPLICATIONS 
   This application claims priority to U.S. Provisional Patent Application Ser. No. 60/845,017 filed Sep. 15, 2006. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to marine boats or vessel hulls utilizing a conventional twin-hull catamaran boat or vessel configuration with a mid-length cavity wherein pressurized air or gas is mechanically induced to provide vessel lift for reduction of total water drag on the hull, thereby reducing the power levels required to attain a specific design speed. This in-turn allows for a reduction of power levels for a given speed thereby reducing the fuel consumption of the designated propulsion units. 
   2. Description of the Prior Art 
   The primary objective in boat or vessel design is to reduce the amount of drag caused by the interaction of the hull with the water surface. Planing hulls are designed so that forward motion of the hull raises the vessel to cause it to ride on a smaller portion of its hull surface resulting in reduced hull-to-water friction. The design of hydrofoil vessels further reduced hull contact with the water by attaching foils to lift the hull surface above the water surface at high speed. Some marine vessels inject a film of air between the vessel&#39;s hull and the water to reduce the hull-to-water friction. One example is illustrated in U.S. Pat. No. 3,191,572 issued to H. A. Wilson in which a tri-hulled vessel has air introduced along the bottom of each hull. This air is allowed to stream freely from the stern of the vessel. U.S. Pat. No. 4,031,841 issued to Bredt also discloses the technology for an air film hull. The Bredt and Wilson hulls still ride with the hull relatively low in the water so that much of the sides of the hulls maintain contact with the water, but the drag between a portion of the bottom is somewhat reduced by a film of air mixed with water. 
   Surface effect ships were an improvement over the air film hulls as the hulls of surface effect ships are raised out of the water by a pressurized air cushion that is partially captured within the hull of the vessel. The prior art of air cushion vessel hull designs include the Harley patent (U.S. Pat. No. 5,570,612) which eliminated the use of flexible seals to contain the air cushion, but this prior art did not properly dispose of the pressurized air cushion to allow for the use of water jet propulsors. The use of water jet propulsors is a critical element for the application of high speed ferry designs in debris-filled waterways. Prior to that, surface effect ships contained the air cushion with flexible seals, which are a rubberized curtain, either all around the vessel as in the case of the hovercraft air cushioned vessels, or across the front and the back of the vessel with thin parallel side hulls that provide a side seal for the air cushion as in the case of surface effect ships. The flexible seals reduce the amount of air lost from the air cushion but create a rough ride even in smooth water. As the surface of the water becomes rougher the flexible seals can be separated from each other. Also, in rough water the flexible seals frequently fail to maintain the air cushion, causing the craft&#39;s hull to drop lower into the water until the seal is regained and the air cushion is reestablished. The loss of the air cushion increases the hull contact with the water increasing the hull-to-water friction and significantly slowing the vessel. Seals are a high maintenance problem with frequent breakage that results in permanent loss of air cushion and a slow ride to the repair yard. Such surface effect ships are disclosed by U.S. Pat. Nos. 5,415,120, and 4,392,445 issued to Donald E. Burg and U.S. Pat. No. 4,523,536 issued to Mark H. Smoot. 
   Notwithstanding the existence of such prior art for surface ships, it remains clear that there is a need for a vessel which will maintain a relatively smooth ride and maintain the air cushion whether the water is smooth or rough without the use of flexible seals. Also, there is a need to improve the stability of surface effect ships which are notoriously unstable in rough water, and enable the introduction of water jet propulsors to minimize damage caused by debris to conventional propeller driven propulsion systems. 
   SUMMARY OF THE INVENTION 
   The present invention relates primarily to a twin-hull catamaran shape with a pair of forward and aft buoyancy/hydrodynamic hull sections with a mid-length hull section that has a cavity to mechanically induce gas or air to provide an efficient, stable, smooth, high speed ride. The quadra-pod air assisted catamaran boat or vessel hull comprises two symmetrical hulls joined by a transverse deck surface. Each hull comprises a bottom, having an exterior surface; and opposing sides, having first and second ends, attached to the bottom and extending upwardly there from, the sides curving inwardly and joining together at the first end to form a bow and being connected together at the second end by a transversely extending transom or step, a generally planar surface, extending inwardly from the bottom generally perpendicular to the longitudinal dimension so that a plane defined by a step separates each catamaran hull into three parts, a bow portion extending forward of the step, an air cavity portion extending rearward of the step, and an aft hull portion extending from the aft end of the air cavity portion to the transom of the vessel. 
   The bow portion of the bottom comprises a port face and a starboard face that are joined together to form a convex V-shape that extends from proximal the bow to the step. The apex of the V-shape defines the keel of the bow portion. The bow portion of the bottom may also possess an appendage for wave-piercing capability depending on the sea state and speed the hull is to be designed for. The port and starboard face each define an angle with a horizontal plane defined as the dead rise angle of the hull. A cross section of the hull generally perpendicular to the longitudinal dimension defines a dead rise angle that lies within a range of 45 degrees to 65 degrees. The dead rise angle decreases rearward aft to no less than 15 degrees as defined by the intersection between the step and the bottom of the bow portion. 
   The mid-length portion of each catamaran hull has a cavity formed therein, the cavity extending rearward from the step of the bow portion, to the intersection with the aft hull portion at the intersection of the aft hull portion and the chine&#39;s, and inwardly from the exterior surface of the sides. The top portion of the cavity is formed by a horizontal plane parallel to the keel. A pressurized air generation means that is well known in the art is connected in fluid flow communication with the air cushion cavity to provide hull lift. 
   The aft portion of the bottom comprises a port face and a starboard face that are joined together to form a convex V-shape that extends longitudinally from the bow of the aft portion to the transom. The apex of the V-shape defines the keel of the bow of the aft portion. The first and second face each defines an angle with a horizontal plane defined as the dead rise angle of the hull. A cross section of the hull generally perpendicular to the longitudinal dimension defines a dead rise angle that lies within a range of 45 degrees to 75 degrees. The dead rise angle running aft decreases to no less than 20 degrees as defined by the intersection between the transom and the bottom of the aft hull portion. 
   Fins or skegs are incorporated between the forward and aft hull sections on each side of each hull at each chine to guide the water flow under the boat or vessel to retain air within the cavity portion of the hull. The enclosure of the air cavity allows air or gas to mechanically be induced to create a pressure that will lift the vessel in order to reduce the resistance of the forward and aft hull sections thereby reducing the amount of power required to drive the design at a specified speed. The end of each fin at the terminus with the intersection of the aft hull with the chine allows the air to be released from the cavity in a way as to prevent interaction with water jet propulsors and also to reduce the wake generated by the boat or vessel hull. 
   The invention accordingly comprises an article of manufacture possessing the features, properties, and the relation of elements which will be exemplified in the article herein-after described, and the scope of the invention will be indicated in the claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a fuller understanding of the nature and object of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings, in which: 
       FIG. 1  is a perspective view of the quadra-pod air assist catamaran boat or vessel hull of this invention. 
       FIG. 2  is a bottom plan view of the invention of  FIG. 1 . 
       FIG. 3  is a centerline elevation view of one of the quadra-pod hulls. 
       FIG. 4  is a sectional elevation view taken along line  4 - 4  of  FIG. 2 . 
       FIG. 5  is a sectional elevation view taken along line  5 - 5  of  FIG. 2 . 
       FIG. 6  is a sectional elevation view taken along line  6 - 6  of  FIG. 2 . 
       FIG. 7  is a sectional elevation view taken along line  7 - 7  of  FIG. 2 . 
       FIG. 7   a  is a sectional elevation view taken along line  7 - 7  of  FIG. 2 . 
       FIG. 8  is a sectional elevation view taken along line  8 - 8  of  FIG. 2 . 
       FIG. 9  is a sectional elevation view taken along line  9 - 9  of  FIG. 2 . 
       FIG. 10  is a sectional elevation view taken along line  10 - 10  of  FIG. 2 . 
       FIG. 11  is a sectional elevation view taken along line  11 - 11  of  FIG. 2 . 
   

   Similar reference characters refer to similar parts throughout the several views of the drawings. 
   DETAILED DESCRIPTION 
   A preferred embodiment for the quadra-pod hull is illustrated in the drawing  FIGS. 1-11  in which the vessel is generally indicated as  10 . Referring first to  FIG. 1  it can be seen that the vessel hull  10  comprises a pair of catamaran hulls  12  that are joined to one another by a deck or cross structure  14 . 
   As shown in  FIG. 2 , each catamaran hull has a longitudinal dimension, and comprises a bottom  16 , that has exterior surfaces  18 , a pair of opposing sides  20  that are attached to the bottom  16  and extend upwardly there from. For the purposes of this specification, the chine  22  defines the line of attachment of the sides  20  to the bottom  16 . The first ends  24  of each side  20  are joined to form the bow  26 , the second mid-length sections  36 , and the third ends  28  are connected to one another by a transom  30  that extend transversely there between. A step  32 , extends inwardly from the bottom  12 , which can be seen most clearly in  FIGS. 3 and 7 , extends inwardly from the bottom  12 , generally perpendicular to the longitudinal dimension. 
   As seen in  FIG. 2 , the step  32  lies in a plane B that defines a bow portion  34  extending forwardly, including the bow  26 , and an air cushion portion  36  extending rearward of said plane to intersect the aft hull portion  50  that extends rearward of said plane to the transom  30 . In the preferred embodiment the bow section  34  comprises 30 to 35 percent of the overall length of the vessel from the bow  24  to the transom  30 , the air cushion portion comprises 30 to 35 percent of the overall length of the vessel from the bow  24  to the transom  30 , and the aft portion  28  comprises 30 to 35 percent of the overall length of the vessel from the bow  24  to the transom  30 . 
   The bow portion  34  of the bottom  16  comprises a first face  38  and a second face  40  that are joined at the keel  42  to form a convex V-shape. Each face,  38  and  40 , forms a dead rise angle, C, with a horizontal plane. At a cross section of the bottom  16  proximal the bow  26 , as shown in  FIG. 5 , the angle C is preferably 55 degrees, however in other embodiments the angle C proximal to the bow  25  may lie within the range of 45 degrees to 65 degrees and still function satisfactorily. In a preferred embodiment, the angle C gradually decreases to no less than 15 degrees at the step  32 . 
   The air cushion portion  36  of the hull  10  has an air cushion cavity  44  formed therein that extends rearward from the step  32  to proximal the aft hull portion  50 . The recess  44  is bounded by the step  32  at the forward end, sloping cavity side surfaces  46 , the aft hull surfaces  50 , and the top of the cavity  48 . In other embodiments, the air cushion cavity  44  may comprise many different shapes that are well known in the art. The shape shown in  FIGS. 8 and 9  is but one example of a shape that works effectively. In a preferred embodiment, the length of the air cushion cavity  44  is greater than the transverse width as measured between the fins  52  at right angles to the longitudinal dimension A. 
   The aft hull portion  50  of the bottom  16  comprises a first face  38  and a second face  40  that are joined at the keel  42  to form a convex V-shape. Each face,  38  and  40 , forms a dead rise angle, D, with a horizontal plane. At a cross section of the bottom  16  proximal the aft hull portion, as shown in  FIG. 9 , the angle D is preferably 55 degrees, however in other embodiments the angle D proximal to the bow  26  may lie within the range of 45 degrees to 75 degrees and still function satisfactorily. In a preferred embodiment, the angle D gradually decreases to no less than 20 degrees at the transom  30 . 
   In a preferred embodiment, the fins  52  extend from a point forward of the step  32  on the chine surface  22  of the bow portion  34 , onto the chine surface  22  of the mid-length portion  36 , and ending at the intersection of the aft hull portion  50  and the chine surface  22 . The starting point of the fins  52  is forward of the step  32  that lies within the range of 3 percent to 10 percent of the overall longitudinal dimension of the vessel  10 . In a preferred embodiment, the fins  52  extend 30 to 35 percent of the overall longitudinal length of the vessel  10 . For example, on a 100 foot long vessel the fins  52  will extend 1 foot forward of the step  32  and extend to 6 inches forward of the intersection of each chine  22  on the aft hull portion  50 . The vertical extent of the fins  52  extends one-half to 1 percent of the overall length of the fins  22 , from the bottom surface  18 , e.g., approximately 6 to 12 inches for a vessel  10  having a 100 foot longitudinal dimension. 
   The portion of each fin  52  that is distal the boat  10  comprises a fin keel portion  54 . The fin keel portions  54  of each fin  52  lie generally in the same plane with one another and generally in the same plane as a portion of the keel  42  of the bow portion of the hull  10  that is proximal to the step  32  and the intersection of the aft hull portion  50  at the chine surface  22 . 
   A pressurized air generation means, shown generally as  58  is preferably mounted within the vessel  10  and is connected by ducting  60  to outlets  62  formed in the top of  48  and the cavity  44 . Devices  58  for supplying air under pressure are well known in the art of surface effect ship design and may be provided as single unit for each hull as shown in  FIGS. 3 and 7 , or multiple units as shown in  FIG. 7   a  in each hull may be used as connected by ducting  60  to outlets  62  in the top of  48  and the cavity  44 . The devices may be operated by their own motors or may be operated by power take-offs from other motors on the vessel  10 . To assist in the direction of flow of pressurized air injected into the cavity, an air dam  63  is provided to prevent the backflow of water into the fan outlet(s)  62  or ducting  60 . The vertical location of the air dam is proximal to the horizontal level with the top of  48  in the cavity  44 . 
   The quadra-pod air assist hull  10  may be constructed of fiber glass, synthetic resins, composites, aluminum, steel, or any other material or combination of materials that are suitable for the purpose. Boats or ships constructed using the quadra-pod hull design disclosed may use any drive method including standard outboard motors for smaller boats and larger inboard gas or diesel engines or turbine engines for large vessels. 
   Having thus set forth a preferred construction for the quadra-pod hull  10  of this invention, it is to be remembered that this is but a preferred embodiment. Attention is not invited to a description of the use of quadra-pod hull  10 . Certainly many different super structures may be constructed on the hull  10  depending on the use for which the vessel is intended, including but not limited to racing craft, pleasure yachts, and for freight and/or passenger transport. 
   The quadra-pod hull  10  discussed below is discussed in relation to a hull  10  that has no restriction on an overall longitudinal dimension. Various size hulls  10  may be constructed with generally proportional dimensions, however, these dimensions may be adjusted depending upon the specific use that is intended for the vessel utilizing the quadra-pod hull  10 . The quadra-pod hull  10  does not incorporate any flexible seals, thereby eliminating the historical problems associated with a conventional surface-effect craft, a rough ride, high maintenance, control problems, high hump drag (meaning ships with flexible seals are hard to get up on the cushion, to get over the hump, which takes a lot of power that is not necessary when the vessel is on the cushion). The quadra-pods hull  10  is a catamaran with twin hulls that each has a mid-length cavity portion  36  that is approximately 30 to 35 percent of the overall length. Each hull  12  has a bow portion  34  that comprises approximately 30 to 35 percent of the overall longitudinal dimension and an aft portion  28  that consists of a 30 to 35 percent of the overall vessel length. 
   The bow portion  34  of each catamaran hull  12  has a V-bottom  16  with a sharp entry proximal the bow  26 , a dead rise of approximately 55 degrees, the dead rise is reduced to no less than 15 degrees proximal the step  32 , easily creating dynamic lift as the vessel&#39;s speed increases so that the vessel easily begins to plane, as boats without air cushions have operated for years. The bow portion  34  is designed to deflect the approaching waves both downward and sideways in a progressive manner over a substantial part of the craft&#39;s length. The water passing beneath the air cavity is consequently modified to be essentially horizontal, even when the quadra-pod hull  10  is operating in significant seas. The advantages of this design, which modifies the flow of the approaching waves before they reach the air cavity portions  36  of each catamaran hull  12 , are considerable. Flexible seals used by conventional surface effect ships are unnecessary, eliminating the high maintenance costs and down time required for repair of flexible seals. Without the modification of the waves to essentially a horizontal configuration, the waves strike the flexible seals of conventional quadra-pod ships causing reduction in cushion volume and variations in the cushion pressure creating additional lift power requirements, and along with bow slamming are the primary factors that can result in a rough ride. The bow portion  34  of the each catamaran hull  12  greatly reduces pitching and spray compared with a conventional surface effect ship. 
   By elimination of the mid-length hull volume with a cavity and mechanically inducing pressurized gas or air into a cavity, the total hull drag is greatly reduced as the air cavity portion  36  of the quadra-pod hull  10  lifts the hull out of the water and significantly reduces the wetted surface of the vessel. The pressurized air cavity, which creates air platform lift over the mid-length area of the hulls  12  dramatically reduces hull resistance and improves intact stability. This combination of hydrodynamic lift and air platform lift to create a highly efficient vessel hull form not previously obtained in prior boat and ship hull designs. Therefore the quadra-pod hull  10  combines both hydrodynamic lift from movement of the vessel through the water as well as dynamic lift with lift from a pressurized air cavity, making it easy for the vessel to reach and maintain plane and yet significantly reduces the drag on the hulls  12  and in-turn reduces required engine power and fuel consumption. 
   Use of twin hulls  12 , each with a separate pressurized air cushion increases intact stability without appreciably increasing the drag. The separated hulls and separated air cushions create a large roll-restoring force which produces a quadra-pod vessel that is not center-of-gravity sensitive. Stiffness and damping in roll are greatly increased because each air cushion acts on the cushion separation arm to provide roll stability. Twin hulls  12  also increase the efficiency of performance at all speeds compared with the design of prior art single cushion surface effect ships that are only designed for efficiency at one speed. Performance improvements also result from air cushion cavities that are greater in length longitudinally rather than transversely which in conjunction with the interconnection geometry of the catamaran hull shapes  10 , chines  22 , and skegs  52  prevent the loss of pressurized air to provide lift of the hull form. 
   Placement of the air cavity  44  too far forward reduces the dynamic lift and exposes the air cushion cavity  44 , which would then require the use of a flexible curtain as in the prior art conventional surface effect ships. Placing the air cushion cavity  44  too close to the bow  26  would increase the drag appreciably. A 30 to 35 percent bow portion  34  combined with a 30 to 35 percent air cavity portion  36  and a 30 to 35 percent stern portion  28  has been found to be a preferred embodiment for the quadra-pod hull  10 . 
   The mid-length hull air cavity  44  must be protected so that water does not enter the air cavity  44  or an unacceptable amount of air escape forward or aft. The sharp entry of the bow portion  34  that gradually reduces to a dead rise of not less than 15 degrees deflects the approaching waves both downward and sideways and modifies the water flow as it approaches the air cavity  44  to relatively horizontal flow. The fins  52  that extend slightly forward of the air cavity  44  and aft to the aft hull portions  50  intersection with the chine surfaces  22  direct small portions of air to the sides which allows the aft hull portions  50  to be fully immersed. The flow of water directed by movement of the boat or vessel between the fins  52  forms the bottom portion of the air cavity  44  which allows mechanically induced gas or air to be trapped to lift the boat or vessel resulting in reduced resistance/drag of the bow and aft hull portions of the catamaran hulls. The immersion of the aft hull portions free of air intrusion allows for the use of water jet propulsors. 
   It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in the above article without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. 
   It is also to be understood that the claims asserted are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall there between.