Abstract:
A combined hull and steering mechanism for a marine vessel has a substantially rectangularly-shaped upper hull joined to a lower hull that is dual-tapered from its sidewalls to both its forward and aft portions. A directional thrust steering mechanism having a pair of vertical rudder blades positioned on either side of a conventional propeller extending from the centerline of the lower hull directs the water from the propeller, thus enabling the vessel to move more efficiently and with greater maneuverability in both forward and reverse directions. The dual-tapered hull permits a significantly better flow of water to and from the propeller and steering mechanism of the vessel, particularly when operating in reverse, thereby allowing the vessel to turn 360° in its own length.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     This invention relates to a combined hull and steering mechanism for marine vessels and particularly for a special purpose marine vessel that is commonly used to move work barges and other similar craft required for the construction of piers, docks and other marine structures, this craft being referred to in the maritime trade as a “pushboat”.  
         [0003]     2. Description of the Related Art  
         [0004]     Pushboats are essential vessels required in the construction of piers, docks and the like. A pushboat must be highly maneuverable and must be able to move other large marine vessels, such as barges, in the typically tight surroundings of a construction project. Pushboats are relatively small and manned by a single operator.  
         [0005]     Pushboats have been used on the aforementioned types of jobs for many years. The name pushboat is derived from a large flat vertical plate that extends across the bow, which can make stable contact with the flat side hull of a barge, floating dock or the like, to provide a broader area of contact, and therefore stability during the maneuvering operation. The distinctive feature of the pushboat is its flat bow surface or prow, which distinguishes it from a tug boat and other work boats that have a more traditional hydrodynamically tapered or pointed bow that is more efficient for forward movement.  
         [0006]     One problem with pushboats, however, is the fact that the flat bow plate limits maneuverability of the boat through water as there is a significant amount of lateral resistance encountered when such a vessel is turned. Typically, additional rudders known as flanking rudders, are required to aide in the steering of pushboats to compensate for this lack of maneuverability. They are positioned outboard and forward of the propeller  
         [0007]     One object of the present invention is to provide a marine vessel which is less resistant to lateral forces of the water when turning and thus has much greater maneuverability and is faster than other marine vessels of similar shape and size.  
         [0008]     Another object of the present invention is to provide a marine vessel having a hull that is configured to allow the vessel to turn in a tighter pattern and to move more efficiently than other marine vessels of similar size and function.  
         [0009]     Still another object of the present invention is to provide a marine vessel which is capable of coming about 180 degrees, and even of turning 360 degrees, in its own length.  
       SUMMARY OF THE INVENTION  
       [0010]     These and other objects and advantages are achieved by the novel pushboat hull of the invention that is comprised of an upper and a lower portion whose shapes differ markedly from each other. The upper portion of the hull which is sometimes referred to as the upper hull, is generally rectangular in shape and overhangs a lower, dual-tapered hull. As used herein, the term “dual-tapered hull” means a hull having side walls that meet by tapering inwardly and are joined at the longitudinal center line, or the line defined by the keel of the boat. The hull rises towards the bow at an angle from a flat bottom, beginning at a transverse line about one-third of the length of the longitudinal axis from the bow of lower hull. The forward end of the lower dual-tapered hull is configured as a flat, triangular surface, which results in lift and less resistance when the vessel is moving forward.  
         [0011]     The novel hull configuration of the invention significantly minimizes the lateral resistance encountered by prior art boats such as those disclosed in U.S. Pat. No. 3,822,661 issued Jul. 9, 1974, U.S. Pat. No. 6,112,687 issued Sep. 5, 2000 and U.S. Pat. No. 6,834,605 issued Dec. 28, 2004. Boats of the prior art generally disclose the concept of implementing a ship hull having two main hull portions that take the form of a relatively flat upper hull mounted above a lower portion formed of a smaller, rounded or cylindrical section attached to the underside of the upper hull.  
         [0012]     However, the combined hull and steering configuration of the present invention is significantly superior to any of the claimed configurations of the prior art. One difference is that the lower portion of the hull is dual-tapered, that is, its oblong shape tapers from its outermost widest section, with the sides intersecting at a generally vertical line at the forward and aft ends. Tapering the aft or rear end of the lower dual-tapered hull permits a significantly better flow of water to the propeller and steering mechanism by drawing water toward the propeller as opposed to away from it as with conventional hull designs that are either generally flat and not tapered at all or are tapered only in the bow or forward end of the hull. This eliminates the need for additional rudders to steer the vessel as are generally used in the prior art. The aft end of the dual-tapered hull also eliminates the need for external supports for the propeller shaft housing, as depicted, for example, in U.S. Pat. No. 3,822,661. This configuration results in improved hydrodynamic flow, decreased lateral resistance and improved maneuverability.  
         [0013]     The dual-tapered configuration is of particular importance when the combination of the partially enclosed directional thrust steering mechanism of the invention is employed to shorten the turning radius and the space required to maneuver the pushboat. A particular advantage of the hull design of the invention is realized when the propeller of the pushboat is reversed, since the tapered aft section allows the forces of the thrust from the propeller to flow either up both sides of the lower hull or to be applied away from, or along either of the side walls of the lower hull portion. This efficiency of operation is not possible where the lower hull transom is flat and extends a significant distance across the width of the aft portion of the hull as is typically found in vessels of the prior art.  
         [0014]     The enclosed directional thrust steering mechanism is adapted for use in combination with a conventional screw propeller. The steering mechanism is comprised of two parallel fin-type blades, one on each side and outboard of a screw propeller. The blades are both connected to a single steering mechanism post. The distance between the blades is sufficient to allow turning of the steering mechanism without contacting the propeller.  
         [0015]     The steering mechanism post or shaft is rotatable about a vertical axis, which is directly above, and perpendicular to the horizontal axis of the screw propeller. A significant portion of the rudder blades extends forward of the vertical axis of the steering mechanism post. Such positioning allows for the thrust of the propeller to be directed more efficiently when said propeller is rotated in the reverse direction.  
         [0016]     In a particularly preferred embodiment, the vertical projection of the axis of rotation of the steering post and attached mechanism passes through plane of rotation of the propeller. The geometry and dimensions of the steering assembly can readily be determined based upon the size of the propeller and its extension from the aft end of the lower hull. The transverse width of the steering assembly must be sufficient to avoid contact with the rotating propeller when the assembly is in the maximum port or starboard position.  
         [0017]     While the submerged dual-tapered hull is designed to minimize lateral resistance, the twin fin directional thrust steering mechanism maximizes the lateral forces needed to turn the vessel in the desired direction.  
         [0018]     It has been found that enclosing the propeller in a tube or other confining structure can result in undesirable cavitation when the propeller rotational speed exceeds a specified rpm value. Cavitation produces vibration and results in a loss of efficiency. Since the type of work performed by pushboats often requires maximum power and corresponding maximum rpm output of the engine, caviation is to be avoided.  
         [0019]     In a preferred embodiment, the area between the lower edges of the twin rudder fins and beneath the propeller is open- to avoid cavitation. This preferred open configuration can be utilized when the pushboat will be working or moored in water whose depth is expected to preclude grounding. If grounding is a possibility during low tide conditions or where the depth is variable or unknown and it is desired to protect the propeller in the event of grounding, a plate can be attached below the propeller and the directional steering assembly. The protective plate is configured to minimize the restriction of water flow and thereby to avoid cavitation. In a preferred embodiment, the plate is detachably installed using releasable fasteners, such as bolts secured to threaded studs or rods that are suspended from one or both of the hulls. Removal of the plate permits easy access to the propeller, its driveshaft and bearing in the event that repairs are required.  
         [0020]     As will be understood from the above, a pushboat or any other marine vessel having a directional thrust steering mechanism as described for a single fixed screw propeller that extends from a dual-tapered lower hull, effectively permits the pushboat to turn 180 degrees, or even 360 degrees, in its own length, a maneuver that is not possible in any known watercraft of the prior art. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]     Preferred embodiments of the invention are further described with reference to the drawings, in which:  
         [0022]      FIG. 1  is a side elevational view of a vessel having a hull and steering mechanism configured in accordance with the present invention;  
         [0023]      FIG. 2  is a bottom view of said vessel;  
         [0024]      FIG. 3  is a front elevational view of said vessel;  
         [0025]      FIG. 4  is a rear elevational view of said vessel;  
         [0026]      FIG. 5  is a side elevational view of a preferred embodiment of the directional thrust steering mechanism;  
         [0027]      FIG. 6  is a rear elevational view of the steering mechanism;  
         [0028]      FIG. 7  is a top plan view of said directional thrust steering mechanism, the top and bottom being similar;  
         [0029]      FIG. 8  is a top plan view, partly in phantom, showing the aft end of the dual-tapered hull with the steering mechanism turned hard to port;  
         [0030]      FIG. 9  is a bottom view of a second embodiment of the invention; and  
         [0031]      FIG. 10  is a rear elevation view of the boat of  FIG. 9 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0032]     The invention is further described with specific reference directed to a combined hull and steering mechanism configured for the special purpose marine vessel referred to as a pushboat. Referring to  FIG. 1 , there is illustrated a pushboat  1  provided with an upper hull portion  10 , which overhangs the lower dual-tapered hull portion  12 . An enclosed directional thrust steering mechanism  14  is positioned between the aft end  18  of the lower dual-tapered hull and the aft end of upper hull portion.  
         [0033]     The upper hull  10  has a forward and aft section, and a top, bottom and sidewalls, it is generally rectangular and flat on the bottom, but may also be rounded in an alternative embodiment (not shown). The forward section of the upper hull rises above the waterline to meet the bow surface  10 A at the outside corners  29  of the upper hull, which eliminates the generally wide, flat submerged bow employed by the prior art. This configuration allows the water to pass under the vessel with a minimum of resistance, eliminating the resulting bow wave and loss of performance characteristics and efficiency when moving in the forward direction that is associated with craft of the prior art. This configuration also reduces lateral resistance while turning and improves maneuverability.  
         [0034]     For the purposes of this description, a vessel having a nominal length L of about 25 feet, a beam W of 10 feet and a draft D of 3 feet is described. The lower hull can be 30 inches deep and the upper hull is submerged about 6 inches. A 210-horsepower diesel engine mounted in the lower hull will provide adequate power for a steel vessel of this configuration.  
         [0035]     As can be readily seen in  FIG. 2 , the lower dual-tapered hull  12  is displaced aft of bow surface  10 A a distance of about four feet or about 15% of the overall length of the vessel. The lower hull is attached to upper hull  10 , as by welding. This reduction in the overall length of the lower hull also greatly reduces lateral resistance encountered when turning the vessel. The forward bottom section  16  of the dual-tapered hull is angled upwardly along a transverse line  17  that is displaced a distance of about one-third of the lower hull&#39;s length from the bow, or about 5.5 feet, to form a substantially triangular section that produces lift when moving in the forward direction and that also serves to substantially reduce lateral resistance when turning as compared to prior art pushboat configurations. The forward bottom section of the dual-tapered hull is best seen in  FIG. 3  and illustrates how it would cut through the water thereby reducing lateral resistance when turning.  
         [0036]     The hydrodynamic shape of the dual-tapered hull  12  allows the water to flow freely past the aft tapered end  18  to the propeller  13  and to enter the area of the steering mechanism, or rudder assembly,  14  as the vessel moves forward.  
         [0037]      FIGS. 4 and 5  depict the positioning of the steering mechanism  14  behind the aft tapered end  18  of the lower hull  12 . The propeller drive shaft  20  extends through a waterproof bearing seal  40  mounted in the lower hull. The propeller is displaced aft of the lower hull a distance that is sufficient to permit rotation of the steering assembly to direct the water from the propeller past the side of the hull in reverse.  
         [0038]     In the pushboat of this example, the rudder blades  15  are about 3.5 feet long and 2.5 feet high. A vertically disposed support strut or post  21 , as shown in  FIGS. 5 and 6 , secures the dual fin steering mechanism  14  in position aft of the dual-tapered lower hull. In the preferred embodiment illustrated, a second supporting cup bearing  23  is positioned below the steering mechanism and is attached to a strut  50  extending from and attached to the lower hull by mechanical fasteners  52  with vibrational dampers  54 , or by welding (not shown).  
         [0039]     As the pushboat  1  is driven through the water by the propeller  13 , the directional thrust steering mechanism  14  becomes effective in two respects. First, as can be seen in  FIGS. 6 and 7 , by having the two fin-like blades  15  positioned parallel on each side of propeller  13 , the thrust from the propeller is concentrated and there is a substantial increase in efficiency and performance. By connecting the parallel blades  15  with relatively thin, flat structural members  22 , the top and bottom portions of the steering mechanism  14  are not adversely affected by restricted water flow between the blades as may be the case in enclosed steering mechanisms of the prior art that employ round or tubular sections. Second, as the pushboat  1  is turned to maneuver, one blade, provides directional thrust by diverting the water displaced by the propeller  13  in the desired direction and the other blade, provides lateral resistance which aids in the turning of the vessel. The combination provides exceptional maneuverability not possible with constructions of the prior art and permits the craft of the invention to complete a 180° turn, or even a 360° turn, on its own length.  
         [0040]     Referring to  FIG. 8 , when the propeller  13  is rotating in the reverse direction, it is significant to note that the steering mechanism  14  can be turned so that the thrust is directed completely to either side of the dual-tapered hull  12  at the aft tapered end  18 . The effect of the dual rudder elements and the directional thrust, when combined with the dual-tapered hull  12  produces a greater degree of maneuverability for the vessel of the invention than has been obtainable with the vessels of the prior art.  
         [0041]     Referring again to  FIGS. 9 and 10 , the optional protective plate  80  is shown positioned below the propeller and attached to the bottom of the lower hull  12  by fastener  82  and to a pair of struts  84  depending from the bottom of upper hull  10  by fasteners  86 . As best seen in  FIG. 9 , the plate  80  is generally triangular and is of sufficient thickness to resist bending upwardly to interfere with the free turning of the twin fins in the event of an impact. In order to further minimize unnecessary structural members extending from the hulls, the struts  84  and fastener  82  can be removably installed when the pushboat is to be operated without the protective plate.  
         [0042]     The hulls of the invention can be constructed of common structural steel plate using techniques and equipment well known and available in boatyards. Fabrication can be accomplished easily and inexpensively, using basic welding procedures and equipment. As will be apparent to one of ordinary skill in the art, no special bending or machining is required. The propulsion engine can be installed in a simple, straightforward manner. The configuration of the hull portions provides for easy access to conventional packing glands and bearings for maintenance or repair. Tankage for fuel and other necessary lubricants can also be positioned for easy access and enables the vessel to be balanced and seaworthy under a variety of sea conditions. Fresh water keel cooling pipes can be mounted under the upper hull portion making them more efficient and less vulnerable to damage in collisions with underwater objects.  
         [0043]     The flat bottom of the dual-tapered hull adds to the stability and seaworthiness of the craft, while also providing a stable platform that keeps the vessel upright when grounded intentionally, or removed to a dry dock or boatyard where it can be placed directly on its bottom surface without special supports or framing. This hull configuration also facilitates easier handling during transport over land by flatbed truck or trailer.  
         [0044]     The invention results in improved fuel economy, better speed, more maneuverability and overall performance, less maintenance, reduced repair costs and a consequent dollar savings in time and labor costs.  
         [0045]     While the configuration described herein is specifically directed to a hull and steering mechanism configuration for a pushboat, nothing disclosed herein should be construed as a limitation to applying the invention to other types of marine vessels.  
         [0046]     While the preferred embodiment of the present invention has been shown and described, it will be understood that this embodiment is provided by way of example only. Numerous variations, changes and substitutions will occur to those of ordinary skill in the art without departing from the spirit and scope of this disclosure of the invention. Accordingly, it is intended that the invention be limited only by the appropriate interpretation of the claims that follow.