Abstract:
A vessel ( 10 ) designed to operate efficiently as both a catamaran and air cushion vessel can travel at low speed (e.g. Froude number (Fn)=0-0.3) in a catamaran or displacement mode and at high speed (e.g. Froude numbers (Fn)=0.3 or more) in an air cushion or dynamically supported mode. The vessel ( 10 ) includes molded catamaran hulls ( 11, 12 ) with parabolic waterlines, a flexible, air cushion seal system ( 16, 17 ), surface piercing propellers ( 20 ) and a propulsion system (e.g. combined diesel and gas turbine). There are preferably auxiliary gas turbines for generating lift air pressure. Forward mounted independently stabilizing foils ( 30 ), can optionally facilitate ride stabilization and load compensation at high and low speeds. The foils also generate transverse roll forces to improve high speed maneuvering.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     Incorporated herein by reference are U.S. patent application Ser. No. 10/661,113, filed 12 Sep. 2003, published as publication no. US2004112268 on 17 Jun. 2004 and International Application No. PCT/US03/28848, filed 12 Sep. 2003, published as publication no. WO2004024552 on 25 Mar. 2004, and those publications. This is a continuation-in-part of both of these prior patent applications. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     Not applicable  
       REFERENCE TO A MICROFICHE APPENDIX  
       [0003]     Not applicable  
       BACKGROUND OF THE INVENTION  
       [0004]     1. Field of the Invention  
         [0005]     The present invention relates to catamaran air cushion ships. More particularly, the present invention relates to an improved surface effect ship or air cushion ship with a catamaran hull that enables low, high and intermediate speeds with improved efficiency.  
         [0006]     2. General Background of the Invention  
         [0007]     The typical side hull geometry that has been employed by surface effect ships is a prismatic, hard-chine planing hull. These types of hulls are inefficient at developing lift and have very high wave making drag characteristics when the ship is off cushion in the displacement mode. Their primary advantages come from their ease of production and their tendency to introduce a degree of dynamic stability at high speeds. In some situations, an intermediate speed that is in between a low displacement mode and a high speed air cushion mode is desirable.  
         [0008]     In general, catamaran air cushion ships, also known as surface effect ships, are known. Examples disclosed in U.S. Patents are listed in the following table. The following table also lists some propeller related art.  
                       TABLE 1                               Issue       U.S. Pat. No.   Title   Date                   1,976,046   Waterfoil   Oct. 9, 1934       2,405,115   Floating Structure   Aug. 6, 1946       3,065,723   Supercavitating Hydrofoils   Nov. 27, 1962       3,077,173   Base Ventilated Hydrofoil   Feb. 12, 1963       3,141,436   Hydrofoil Assisted Air   Jul. 21, 1964           Cushion Boat       3,458,007   Captured Air Bubble (CAB)   Jul. 29, 1969           Ground Effect Machine       3,621,932   Gas-Cushion Vehicles   Nov. 23, 1971       3,917,022   Twin Cushion Surface Effect   Nov. 4, 1975           Vehicle       3,987,865   Gas-Cushion Vehicle Skirt   Oct. 26, 1976       4,469,334   Sealing System For The Air   Sep. 4, 1984           Cushion Of An Air-Cushion           Vessel       4,489,667   Surface Effect Ship Seals   Dec. 25, 1984       4,506,618   Propeller And Keel   Mar. 26, 1985           Arrangement For Surface           Effect Ships       4,535,712   Variable Air Cushion Mode   Aug. 20, 1985           Vehicle       4,543,901   Surface Effect Ship Air   Oct. 1, 1985           Cushion Seal System       4,646,866   Surface Effect Type, Side   Mar. 3, 1987           Keel Vessel Fitted With An           Improved Forward Buoyancy           Cushion Seal Apparatus       4,660,492   Catamaran Air Cushion Water   Apr. 28, 1987           Vehicle       4,708,077   Hull Shapes For Surface   Nov. 24, 1987           Effect Ship With Side Walls           And Two Modes Of           Operation       4,714,041   Structure of surface effect   Dec. 22, 1987           ship with side walls       4,739,719   Movable bow seal air ride   Apr. 26, 1988           boat hull       4,767,367   Integrated Combination   Aug. 30, 1988           Propeller Drive Shaft           Fairing and Water Intake           Sea Chest Arrangement, For           High Speed Operating Marine           Craft       5,651,327   Displacement, Submerged   Jul. 29, 1997           Displacement, Air Cushion           Hydrofoil Ferry Boat       5,711,494   Aero-Hydroglider   Jan. 27, 1998       5,934,215   Stabilized Air Cushioned   Aug. 10, 1999           Marine Vehicle       6,293,216   Surface Effect Ship (SES)   Sep. 25, 2001           Hull Configuration Having           Improved High Speed           Performance and Handling           Characteristics       6,439,148   Low-Drag, High-Speed Ship   Aug. 27, 2002       6,526,903   High speed M-shaped boat hull   Mar. 04, 2003       6,609,472   Stable efficient air   Aug. 26, 2003           lubricated ship       2003/0000440   Air Assisted Landing Craft   Jan. 02, 2003                  
 
         [0009]     Incorporated herein by reference are U.S. Pat. Nos. 4,767,367; 6,293,216; and 6,439,148. These three patents relate generally to surface effect ships or hovercraft.  
         [0010]     Also incorporated by reference is the following:  
         [0011]     JOHN LEWTHWAITE, “The PACSCAT Concept and its application to Fast Landing Craft”, presented at MACC Multi Agency Craft Conference 2002, The Pulse of Technology, 18-20 Jun. 2002, Naval Amphibious Base Little Creek, Norfolk (19 pages)  
       BRIEF SUMMARY OF THE INVENTION  
       [0012]     The present invention comprises a vessel designed to operate as both a catamaran and an air cushion vessel. This hybrid catamaran air cushion ship has several advantages over previous air cushion and surface effect ship designs. It will be able to efficiently travel at low speeds (Froude number (Fn)=about 0-0.4) in the catamaran or displacement mode. It will also have the ability to operate efficiently in the air cushion or dynamically supported mode at high speeds (Froude number (Fn)=about 0.4 and greater) and with the ability to operate at all speeds. Any number of intermediate dynamic support modes can be achieved by throttling the lift fan system that supplies pressurized air to the air cushion.  
         [0013]     It will be able to efficiently travel at low speeds (e.g. about 0-20 knots (0-37 km/hour)) in the catamaran or displacement mode. It will also have the ability to operate in the air cushion or dynamically supported mode at high speeds (e.g. about 50 knots (93 km/hour) and greater) and with the ability to operate at all speeds. The air cushion can also be used to reduce the ship&#39;s already shallow static draft from, for example, approximately five meters to less than one meter. This ability decreases underwater signatures and has been proven in several full-scale tests to improve survivability in the event of a mine encounter.  
         [0014]     This design concept departs from previous surface effect ships in one key area. With very few exceptions, the surface effect vessels built to date have been designed to optimize high speed performance. The vessel of the present invention will operate efficiently at high speeds, but will also be able to operate efficiently in the lower speed regime.  
         [0015]     This multi-mode operation capability will enable the marine vessel of the present invention to adapt to sea conditions and operate for extended periods without refueling.  
         [0016]     The marine vessel of the present invention features molded catamaran hulls with parabolic waterlines, a flexible, air cushion seal system, an independently powered lift fan (air cushion) system, surface piercing propellers (optionally controllable pitch) and a power plant for each propeller (e.g. combined diesel and gas turbine propulsion system).  
         [0017]     Lift air pressure can be generated, for example, by auxiliary gas turbines or diesels. Intermediate operating modes that are in between displacement mode and air high speed air cushion mode can be achieved by varying power to the lift fan system. Forward mounted lifting foils may be used to facilitate ride stabilization and load compensation, at high and low speeds. These foils may also be used to generate transverse roll forces to improve high speed maneuvering.  
         [0018]     The vessel of the present invention can displace e.g. up to 2,400 long tons, but is scalable and may be manifested in lesser or greater displacements. A vessel in this displacement range, can be, for example, approximately 90 m in length, with about a 30 m beam. Speeds cited earlier would be consistent with this size vessel.  
         [0019]     The concept of the hybrid catamaran air cushion ship of the present invention combines an improved, specially configured catamaran design with equally viable concepts in air cushion vehicle technology. The side hulls of the present invention are designed to be as efficient as possible, by reducing wave making resistance. The marine vessel of the present invention provides superior performance via lower wave marking drag at all speeds. Total resistance is further reduced at high speeds, through reductions in wetted surface area resulting from the lift provided by the air cushion. To accomplish this task effectively, the present invention provides several features.  
         [0020]     The side hulls of the present invention are preferably molded (rounded) forms featuring parabolic waterlines and semi-elliptical cross sections (see  FIGS. 6-7 ). These forms minimize the characteristic wave trains associated with low speeds and have been shown to have superior drag characteristics at both low and high speeds.  
         [0021]     The present invention may optionally employ small lifting surfaces to provide load compensation, ride control and high-speed stabilization. These surfaces can take the form of two, independently controlled, wing sections mounted port and starboard below the waterline on the side hulls (e.g., inboard and forward). Their primary task is to provide ride control at all speeds but they will also provide high-speed stability, enhancing both directional control and maneuvering.  
         [0022]     A hybrid hullform was designed, using slender forms for the sidehulls rather than the long planing bodies used for most surface effect ships. The sidehull depth was set to provide a cross structure (wet deck) clearance (e.g. two meters) above the water, enabling operation as a catamaran, with some allowance for future weight growth.  
         [0023]     The lift system and air cushion seals provide additional wet deck clearance (of, e.g., five meters) when on-cushion (when the vessel is operated in conjunction with a pressurized air cushion), resulting in a low keel draft (e.g., about one meter) in calm water conditions.  
         [0024]     The marine vessel of the present invention can be operated with varying levels of air pressure, with the advantage of improving sea keeping. It is feasible to run in catamaran mode and then transition to the air cushion mode while underway at high speeds. This feature avoids high drag transition speeds of prior art surface effect ships.  
         [0025]     The propulsor is preferably designed for high efficiency in a low speed mode and high speed mode as well as numerous intermediate modes. Propellers can be used as propulsors, propellers being preferred across the entire speed range. To be efficient at high speeds, a propeller preferably operates in the partially submerged mode to avoid prohibitively high drag from the hub and related support structure. Because of the change in keel immersion as the ship goes from off cushion to on cushion, a stern-mounted propeller can be arranged to naturally operate fully submerged in the catamaran mode and surface piercing in the surface effect ship mode. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0026]     For a further understanding of the nature, objects, and advantages of the present invention, reference should be had to the following detailed description, read in conjunction with the attached drawings which are identified as follows:  
         [0027]      FIG. 1  is a perspective view of the preferred embodiment of the apparatus of the present invention;  
         [0028]      FIG. 2  is a side view of the preferred embodiment of the apparatus of the present invention showing the displacement mode;  
         [0029]      FIG. 3  is a side view of the preferred embodiment of the apparatus of the present invention showing the high speed, planing mode;  
         [0030]      FIG. 4  is a rear perspective view of the preferred embodiment of the apparatus of the present invention showing the high speed, planing mode;  
         [0031]      FIG. 5  is a sectional view taken along the lines  5 - 5  of  FIG. 2 ;  
         [0032]      FIG. 6  is a sectional view taken along the lines  6 - 6  of  FIG. 5 ;  
         [0033]      FIG. 7  is a sectional view taken along the lines  7 - 7  of  FIG. 5 ;  
         [0034]      FIG. 8  is a sectional, end view taken along the lines  8 - 8  of  FIG. 5 ;  
         [0035]      FIG. 9  is a fragmentary perspective view of the preferred embodiment of the apparatus of the present invention illustrating the propulsion system for one of the hulls;  
         [0036]      FIG. 10  is a front view of the preferred embodiment of the apparatus of the present invention showing the displacement mode;  
         [0037]      FIG. 11  is a rear view of the preferred embodiment of the apparatus of the present invention showing the displacement mode; and  
         [0038]      FIG. 12  illustrates multiple intermediate waterlines that can be achieved in intermediate modes that are in between the low speed displacement and high speed air cushion modes. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0039]     The marine vessel of the present invention is designed to operate as both a catamaran and air cushion vessel. The hybrid catamaran air cushion ship of the present invention is designated generally by the numeral  10  in  FIGS. 1-4 . Marine vessel  10  has several advantages over previous air cushion and surface effect ship designs. It will be able to efficiently meet the demands of the low speed (Froude number 0-0.4) requirements in the catamaran or displacement mode (see first water line, numeral  27  in  FIG. 2 ). The vessel  10  of the present invention will also have the ability to operate in the air cushion or dynamically supported mode, (see second water line, numeral  28  in  FIG. 3 ) where it will meet the high speed (Froude numbers 0.4 and higher) performance targets and provide the ability to operate in extreme sea states.  
         [0040]     Vessel  10  will be able to efficiently meet the demands of the low speed (e.g. 0-20 knots (0-37 km/hour)) requirements in the catamaran or displacement mode (see first water line, numeral  27  in  FIG. 2 ). The vessel  10  of the present invention will also have the ability to operate in the air cushion or dynamically supported mode, (see second water line, numeral  28  in  FIG. 3 ) where it will meet the high speed (e.g. 50 knots (93 km/hour) or higher) performance targets and provide the ability to operate in extreme sea states. In  FIG. 12 , the numerals  31  show that several intermediate water lines can be achieved, each in between the first and second water lines  27 ,  28 . Such an intermediate water line  31  can be selected for example in rough seas or when a reduced wake is desired.  
         [0041]     The air cushion can be used to reduce the ship&#39;s static draft (from for example approximately five meters to for example less than one meter). This ability decreases underwater signatures and has been proven in several full-scale tests to improve survivability in the event of a mine encounter.  
         [0042]     Hybrid catamaran air cushion ship  10  has a catamaran hull defined by port hull  11  and starboard hull  12 . The vessel  10  provides a bow  13  and stern  14 . Platform  15  is connected to and spans between the port hull  11  and starboard hull  12 . The catamaran hull and platform  15  carry a powered lift fan system (e.g. gas turbine) for forming an air space between hulls  11 ,  12  and seals  16 ,  17 . Such powered lift fan systems are known in the art. The horsepower to the lift fan system can be varied using a throttle for selecting any number of intermediate water lines  31  of  FIG. 12 .  
         [0043]     Each hull  11 ,  12  can optionally be provided with hydrofoil stabilizers  30  (see, e.g.,  FIGS. 10 and 11 ), being very stable without hydrofoil stabilizers. At bow  13 , forward seal  16  can be in the form of a plurality of individual finger seals  25 . Such a seal  16  can be seen for example in prior U.S. Pat. Nos. 3,621,932; 3,987,865; and 4,646,866, each incorporated herein by reference. Forward seal  16  includes preferably a plurality of between about four and ten (preferably eight) fingers or elements  25 . These can be optionally retracted when low speed operation ( FIG. 2 ) is required. However, the retraction feature is optional because tests show that there is no measurable drag penalty with the seals  16 ,  17  dragging in the water during low speed operation. These fingers  25  can also be used to generate transverse roll forces to improve high speed maneuvering.  
         [0044]     An aft seal  17  is provided at stern  14  as shown in  FIG. 11 . The forward and aft seals  16 ,  17  in combination with the catamaran hulls  11 ,  12  provide a space that can be pressurized with air for providing an air cushion that supports the ship  10  in a high speed mode shown in  FIG. 3 . In the mode of  FIG. 3 , the second water line  28  extends through the center of rotation of propellers  20 , enabling the air cushion ship  10  of the present invention to attain high speeds of for example in excess of 50 knots (93 km/hour) with minimal resistance. Propellers  20  are designed to operate in a surface piercing mode and/or fully wetted mode (where the propellers  20  are typically fully submerged) and can for example be driven by a diesel or a gas turbine power plant or a combined diesel and gas turbine power plant.  
         [0045]     In a slow travel mode of for example between about 0 and 20 knots (0 and 37 km/hour), vessel  10  can travel in a displacement mode that is shown in  FIG. 2 . That vessel  10  is in the displacement mode in  FIG. 2  can be seen by observing first water line  27 . In the displacement mode of  FIG. 2 , the propellers  20  are fully submerged as is each of the rudders  23 ,  24 . In the displacement mode of  FIG. 2 , the forward and aft seals  16 ,  17  can be retracted or removed.  
         [0046]     In  FIGS. 5-9 , each of the hulls  11 ,  12  is a smooth hull providing a smooth outer surface that does not have any hard chines. Such a hull construction as shown in  FIGS. 5-9  is very efficient at low speeds. Each of the port hull  11  and starboard hull  12  has a smooth curved bottom  18  and a pair of opposed smooth side walls  19 ,  21 . The side walls  19 ,  21  include outer side wall  19  and inner side wall  21 . The side walls  19 ,  21  can be generally vertically oriented as shown in  FIGS. 6 and 7 . These hulls  11 ,  12  preferably have parabolic waterlines.  
         [0047]     A propeller shaft housing  22  that is tubular in shape can extend from the rear of each of the port and starboard hulls  11 ,  12  as shown in  FIGS. 2, 3 ,  8 , and  9 . Each hull  11 ,  12  has its own surface piercing propeller  20 . Port hull  11  provides port rudder  23 . Starboard hull  12  provides starboard rudder  24 .  
         [0048]     A deck area  26  can be provided that includes a super structure  29 . This deck area  26  can provide a hangar, flight deck, and a plurality of hatches to enable numerous uses for the ship. It is able to operate efficiently at high speeds, but is also able to operate efficiently in the lower speed regime.  
         [0049]     The hulls  11 ,  12  can be made of aluminum, steel, composite materials, or any other suitable material which will be apparent to those of ordinary skill in this art.  
         [0050]     The following is a list of suitable parts and materials for the various elements of the preferred embodiment of the present invention.  
       Parts Lists  
       [0051]    
       
         
               
               
             
           
               
                   
               
               
                   
               
               
                 Parts Number 
                 Description 
               
               
                   
               
             
             
               
                 10 
                 hybrid catamaran air cushion 
               
               
                   
                 ship 
               
               
                 11 
                 port hull 
               
               
                 12 
                 starboard hull 
               
               
                 13 
                 bow 
               
               
                 14 
                 stern 
               
               
                 15 
                 platform 
               
               
                 16 
                 forward seal 
               
               
                 17 
                 aft seal 
               
               
                 18 
                 curved bottom 
               
               
                 19 
                 outer side wall 
               
               
                 20 
                 propeller 
               
               
                 21 
                 inner side wall 
               
               
                 22 
                 propeller shaft housing 
               
               
                 23 
                 port rudder 
               
               
                 24 
                 starboard rudder 
               
               
                 25 
                 bow seal element 
               
               
                 26 
                 deck area 
               
               
                 27 
                 first water line (displacement 
               
               
                   
                 mode) 
               
               
                 28 
                 second water line (planing mode) 
               
               
                 29 
                 superstructure 
               
               
                 30 
                 foil stabilizer 
               
               
                 31 
                 intermediate water line 
               
               
                   
               
             
          
         
       
     
         [0052]     All measurements disclosed herein are at standard temperature and pressure, at sea level on Earth, unless indicated otherwise.  
         [0053]     The foregoing embodiments are presented by way of example only; the scope of the present invention is to be limited only by the following claims.