Abstract:
An improved watercraft hull providing stability and maneuverability in turns. The hull may include a longitudinal centerline extending from bow to stern, a first and second transverse air channel that are fluidly isolated from the rest of the hull, the first and second air channels separating the hull into a bow planing portion, a middle planing portion, and a stern planing portion, a first plurality of strakes protruding from the bow planing portion, a second plurality of strakes protruding from the middle planing portion, and a third plurality of strakes protruding from the stern portion. The hull may also include a V-shaped keel portion at the bow portion centerline, and a flattened hull portion at the stern portion centerline having a deadrise angle of 0°, the flattened hull portion being disposed between and directly adjacent to two adjacent longitudinal elements of the third plurality of longitudinal elements.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     n/a 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     n/a 
     FIELD OF THE INVENTION 
     The present invention relates to a watercraft hull providing increased stability and maneuverability during turns. 
     BACKGROUND OF THE INVENTION 
     Watercraft such as high-speed powerboats typically include any of a variety of design features to improve speed, directional stability, and maneuverability. High-speed powerboats typically use dynamic lift, referred to as planing, to reduce resistance created by wave generation and to increase speed. Further, such watercraft often incorporate features to improve directional stability and control during operation. 
     One class of commonly used watercraft hull is the planing hull (for example, as shown in prior art  FIGS. 1A and 1B ), which is configured to create positive dynamic pressure so that its draft, or vertical distance to which the hull&#39;s keel extends below the waterline, decreases as the speed of the watercraft increases. In other words, a portion of the hull loses contact with the water, or lifts out of the water. The degree by which the front or fore portion of a hull lifts out the water is referred to as the trim angle. Dynamic lift reduces the wetted surface of the hull and, therefore, also reduces drag. However, planing hulls generally suffer from a resistance paradox. At speeds from a standstill to a speed about equal to 1.5 times the waterline length of the watercraft (“transition speed”), the watercraft is in “displacement mode,” meaning that it has not yet reached planing speed and is displacing water as it moves forward. After reaching the transition speed, the watercraft goes into a “transition mode,” in which it is no longer operating in displacement mode or planing mode. Within transition mode, the watercraft has a pronounced bow-up trim. As speed continues to increase, the watercraft moves out of the transition mode and into “planing mode,” in which the trim levels out and the bow of the watercraft lowers somewhat (that is, the trim angle decreases). As the trim angle decreases, the resistance increases linearly with the dynamic pressure, which increases exponentially. This results in extremely high power requirements for very small increases in speed when trim angles are less than about 3 degrees. 
     Stepped planing hulls were developed to overcome this problem (for example, as shown in prior art  FIG. 2 ). Stepped hull designs incorporate transverse discontinuities, or “steps,” aft of the watercraft&#39;s center of gravity and center of pressure. These steps are generally transverse or substantially transverse (perpendicular to the watercraft&#39;s centerline), and break the one large, low-aspect-ratio planing hull into multiple high-aspect-ratio planing surfaces, thereby making the hull more efficient. Further, by providing multiple planing surfaces, the trim angle variation with speed is essentially eliminated, breaking the resistance paradox encountered with non-stepped or prismatic planing hulls. A stepped planing hull may be operated with the least drag and the optimal trim angle under all speeds. This makes the resistance increase more linearly with speed, rather than exponentially, and enables the boat to reach much higher speeds, or operate at higher efficiencies than the non-stepped planing hull. 
     However, the steps of a stepped hull cause a reduction in the wetted area of the hull at high speeds. Although this is favorable for speed and efficiency, it can adversely affect the directional stability and maneuverability of the watercraft. The more the wetted area of the hull is reduced, the more susceptible the watercraft becomes to yawing or uncontrolled turning at high speeds. In order to reintroduce yaw stability, some stepped hull watercraft include features such as strakes and pads, but these have largely been ineffective. 
     Other stepped hull watercraft include transverse air channels incorporated into the steps, which introduce air to the stern, thereby making the watercraft faster and more efficient than a non-stepped hull (for example, as shown in prior art  FIG. 3 ). In some stepped hulls, air is sucked into the transverse cavities, from where it flows into the stern portion of the boat, toward the transom. The air beneath the stern also creates lift and reduces friction between the hull and the water. Essentially, a portion of the stern rides on a cushion of air. The reduction in wetted hull surface area and the resulting reduction in friction mean that the watercraft moves more easily in the water, thereby improving efficiency of the craft. However, this also means that the stern portion of the hull becomes “slippery,” which can lead to handling, stability, and maneuverability difficulties. Further, although stepped hull designs that incorporate air channels that allow for longitudinal air flow may improve efficiency, the resulting air on the stern channels may introduce air into the water flow at the propeller and thereby reduce propeller performance and decrease propulsive efficiency, thereby offsetting gains in overall efficiency. 
     It is therefore desirable to provide an improved stepped hull design that increases stability and maneuverability of a watercraft, while maintaining propeller performance and propulsive efficiency. 
     SUMMARY OF THE INVENTION 
     The present invention advantageously provides an improved hull and method for providing increased stability and maneuverability to a watercraft hull. In one embodiment, the watercraft hull may include a bow portion, a stern portion, and a longitudinal centerline therebetween, a plurality of longitudinal elements protruding from the hull, a flattened hull portion at the centerline in the stern portion having a deadrise angle of 0°, and a first keel ridge portion at the centerline in the bow portion having a deadrise angle greater than 0°. The plurality of longitudinal elements may include a first pair of longitudinal elements, a second pair of longitudinal elements, and a third pair of longitudinal elements, the first pair being closest to the centerline. The flattened hull portion may be disposed between the first pair of longitudinal elements. Further, the hull may include a middle portion disposed between the bow portion and the stern portion, a first air channel having a first inlet and a second inlet, the first air channel being transverse to the centerline, and a second air channel having a third inlet and a fourth inlet, the second air channel being transverse to the centerline. The first air channel may be in fluid communication only with the first and second inlets, and the second air channel being in fluid communication only with the third and fourth inlets. The first and second air channels may be fluidly isolated from the rest of the hull. The watercraft hull may further include a second keel ridge portion at the centerline in the middle portion having a deadrise angle of 0°, and the second keel ridge portion at the centerline in the middle portion may have a deadrise angle of 0°. The first and second air channels may divide the hull into a first planing portion in the bow portion, a second planing portion in the middle portion, and a third planing portion in the stern portion. The first planing portion may include a first set of protruding longitudinal elements, the second planing portion may include a second set of protruding longitudinal elements, and the third planing portion may include a third set of protruding longitudinal elements. Further, each of the first, second, and third sets of longitudinal elements may include an inner pair of longitudinal elements, a middle pair of longitudinal elements, and an outer pair of longitudinal elements. The inner pair of longitudinal elements in the third set of longitudinal elements may be closer to the centerline than the inner pair of longitudinal elements in the first and second sets of longitudinal elements. The first keel ridge portion may be disposed between the inner pair of the first set of longitudinal elements, the second keel ridge portion may be disposed between the inner pair of the second set of longitudinal elements, and the flattened hull portion may be defined by the second air channel on a first side and the inner pair of the first set of longitudinal elements on a second and third side. The watercraft may further include a first port deadrise hull portion, a first starboard deadrise hull portion, a second port deadrise hull portion and a second starboard deadrise hull portion, a third port deadrise hull portion, and a third starboard deadrise hull portion, each having a deadrise angle greater that 0°. Additionally, the first keel ridge portion, the first port deadrise portion, and the first starboard deadrise portion may be disposed between the inner pair of first set of longitudinal elements, the second keel ridge portion, the second port deadrise portion, and the second starboard portion may be disposed between the inner pair of second set of longitudinal elements, and the flattened hull portion may be disposed between and directly adjacent to the inner pair of third set of longitudinal elements. Each longitudinal element may include a first lateral surface, a second lateral surface, and a face, and the face may have a 0° deadrise, and the first and second lateral surfaces may be substantially orthogonal to the face. The watercraft hull may further include a port sidewall and a starboard sidewall, wherein each of the first, second, and third sets of longitudinal elements include a port outermost longitudinal element and a starboard outermost longitudinal element, and the port sidewall may define the first face of the port outermost longitudinal element and the starboard sidewall may define the second face of the starboard outermost longitudinal element. 
     In another embodiment, the watercraft hull may include a bow, a stern, and a longitudinal centerline extending therethrough; a first transverse air channel and a second transverse air channel, the first and second air channels separating the hull into a bow planing portion, a middle planing portion, and a stern planing portion; a first plurality of longitudinal elements protruding from the bow planing portion, a second plurality of longitudinal elements protruding from the middle planing portion, and a third plurality of longitudinal elements protruding from the stern portion; a first port deadrise hull portion, a first starboard deadrise hull portion, a second port deadrise hull portion and a second starboard deadrise hull portion, a third port deadrise hull portion, and a third starboard deadrise hull portion, each having a deadrise angle greater that 0°; a V-shaped keel portion at the centerline in the bow portion having a deadrise angle greater than 0°, the V-shaped keel portion, the first port deadrise portion, and the first starboard deadrise portion being disposed between two adjacent longitudinal elements of the first plurality of longitudinal elements; a flattened keel portion at the centerline in the middle portion having a deadrise angle of 0°, the flattened keel portion, the second port deadrise portion, and the second starboard deadrise portion being disposed between two adjacent longitudinal elements of the second plurality of longitudinal elements; and a flattened hull portion at the centerline in the stern portion having a deadrise angle of 0°, the flattened hull portion being disposed between an directly adjacent to two adjacent longitudinal elements of the third plurality of longitudinal elements. The first and second transverse air channels may be fluidly isolated from the rest of the hull. 
     The method may include providing a watercraft including a hull having a longitudinal centerline; a first air channel transverse to the centerline and a second air channel transverse to the centerline, the first and second air channels separating the hull into a bow portion, a middle portion, and a stern portion, and the first and second air channels being in fluid communication with atmospheric air; a first plurality of strakes protruding from the bow portion, a second plurality of strakes protruding from the middle portion, and a third plurality of strakes protruding from the stern portion, each of the first, second, and third pluralities of strakes having a port side innermost strake and a starboard side innermost strake; and a V-shaped keel portion in the bow portion, a flattened keel portion in the middle portion, and a flattened hull portion in the stern portion, the flattened hull portion having a deadrise of 0° and being directly adjacent to the port and starboard innermost strake of the third plurality of strakes; moving the watercraft in a first direction to create a vacuum within the first and second air channels, the vacuum drawing atmospheric air into the first and second air channels; and retaining a volume of atmospheric air within the first and second air channels during movement of the watercraft in the first direction. Each strake may include a first lateral surface, a second lateral surface, and a face, and the face may have a deadrise of 0°. The method may further comprise turning the watercraft in a second direction; and generating transverse pressure on at least one of the first and second lateral surface of each strake. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of the present invention, and the attendant advantages and features thereof, will be more readily understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein: 
         FIG. 1A  shows a cross-sectional view of a stylized representation of a planing hull as is currently known in the art; 
         FIG. 1B  shows a stylized representation of a planing hull partially lifting out of the water as speed increases; 
         FIG. 2  shows a perspective view of a stylized representation of a stepped hull as is currently known in the art; 
         FIG. 3  shows a perspective view of a stylized representation of a stepped hull having air channels as is currently known in the art; 
         FIG. 4  shows a bottom view of an improved stepped hull in accordance with the present invention; 
         FIG. 5  shows a side view of an improved stepped hull in accordance with the present invention; 
         FIG. 6  shows a stylized representation of a cross-sectional view of an air channel; 
         FIG. 7  shows a perspective view of an improved stepped hull in accordance with the present invention; 
         FIG. 8A  shows a cross-sectional view the bow portion of an improved stepped hull in accordance with the present invention; 
         FIG. 8B  shows a cross-sectional view the stern portion of an improved stepped hull in accordance with the present invention; 
         FIG. 9  shows a rear view of an improved stepped hull in accordance with the present invention; 
         FIG. 10  shows a bottom view of a stylized representation of the bottom of an improved stepped hull in accordance with the present invention, showing the flow of air and water over the hull bottom; 
         FIG. 11  shows a cross-sectional view of the stern portion of an improved stepped hull during a turning maneuver; 
         FIG. 12  shows an overhead stylized representation of a stepped hull watercraft known in the art during a turning maneuver; and 
         FIG. 13  shows an overhead stylized representation of an improved stepped hull in accordance with the present invention during a turning maneuver. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to  FIGS. 1-3 , stylized representations of a prismatic planing hull, a stepped planing hull, and a stepped planing hull including air channels, as currently known in the art, are shown. These hulls are discussed in the Background section above. Each of the hulls  10  in  FIGS. 1-3  generally includes a hull bottom  12  that includes a keel  14 , a deadrise  16  on either side of the keel  14 , a chine  18  at the interface between the deadrise  16  and a sidewall  20 , a bow portion  22 , a stern portion  24 , a transom  26  in the stern portion, and a centerline  28  running between the bow portion  22  and the stern portion  24 . The stepped hulls  10  shown in  FIGS. 2 and 3  also include one or more steps  30 , the hull  10  of  FIG. 3  further including one or more air channels  32 . Air movement through commonly known stepped hulls is depicted using arrows in  FIGS. 2 and 3 . As shown in  FIGS. 2 and 3 , a volume of air may enter into the steps  30  and/or air channels  32  and then flow longitudinally along the stern portion  24  of hull bottom  12  toward the transom  26 . 
     As used herein, the term “substantially” may include a tolerance of 10% or less. For example, a line that is “substantially parallel” to another may be offset from an absolutely parallel line by 10° or less. 
     Referring now to  FIG. 4-11 , an improved stepped hull in accordance with the present invention is shown. The hull  40  may be part of a speedboat, a fishing boat, or any other suitable watercraft (also referred to as a “boat” or “vessel”). The hull  40  of  FIGS. 4-11  may generally include a hull bottom  42 , which may include a keel  44 , a deadrise portion  46  on either side, that is, port  48  and starboard  50  (as viewed from below the hull  40 , as shown in  FIG. 4 ), of the keel  44 , one or more chines  58  at the intersection of the deadrise portions  46  and the sidewalls  60 , a bow portion  62 , a middle portion  64 , a stern portion  66 , and a transom  68  in the stern portion  66 . The hull  40  may also include a centerline  70  that runs along the hull&#39;s longitudinal axis from the bow portion  62  to the stern portion  66 . The hull  40  of  FIGS. 4-11  may also include one or more steps  72  and one or more air channels  74 ,  76  integrated into the one or more steps  72 , and a plurality of strakes  78 ,  80 ,  82  that protrude from the hull bottom  42 . The deadrise portion  46  on either side of the centerline  70  may be interrupted by the plurality of protruding strakes  78 ,  80 ,  82 , such that a longitudinal portion of deadrise hull  46  is disposed between each set of adjacent strakes  78 ,  80 ,  82 . 
     The bow portion  62  of the hull  40  may include a V-shaped keel  44 A that gradually transitions to a flattened keel  44 B within the aft portion  84  of the bow portion  62 , just forward of a first transverse air channel  74  (for example, as shown in  FIGS. 4 ,  7 , and  9 ). At least at the fore portion  85  of the bow portion  62 , the V-shaped keel  44 A may take on the shape of the deadrise portion  46  on either side, thus giving the keel portion  44 A a deadrise angle that is greater than 0°. That is, the deadrise portions  46  may slope inward toward the centerline  70  at meet at an acute angle, forming the V-shaped keel portion  44 A. As the keel  44  transitions from the fore portion  85  to the aft portion  84  of the bow portion  62 , the deadrise portions  46  terminate at a flattened keel portion  44 B of increasing width, the flattened keel  44 B itself having a deadrise angle of 0°. The term “deadrise” may refer to the angle that is formed between an imaginary horizontal line and the hull at any given point. So, the flattened keel  44 B having a deadrise of 0° may mean that the flattened portion is horizontal without any angle of separation from the horizontal line. The adjacent deadrise portions  46  of the hull bottom  42 , on the other hand, are separated from the horizontal line by an angle α that is greater than 0° (for example, as shown in  FIG. 9 ). Further, the angle α of the deadrise portions  46  from horizontal may be discontinuous, that is, change at one or more locations, along the length of the hull  40 . 
     The bow portion  62  may further include a plurality of longitudinal strakes  78  protruding from the deadrise portion  46  of the hull bottom  44 , each having a first end  86  and a second end  88 . As a non-limiting example, six strakes  78 A,  78 B,  78 C are shown in  FIGS. 4-11 . The keel  44  may be disposed between the two innermost strakes  78 A. Each of the outermost strakes  78 C may define the chine  58  between the deadrise portions  46  and the sidewalls  60 . The first end  86  of each strake  78  may be located at or in contact with the keel  44 A in the fore portion  85  of the bow portion  62 , and the second end  88  of each strake  78  may terminate at the first transverse air channel  72 . As shown, for example, in  FIG. 4 , the longitudinal strakes  78  may be generally parallel to the centerline  70  of the hull  40 , except for the slight curvature required for the first end  86  of each strake  78  to meet the keel  44 . Further, each strake  78  may be tapered from the second end  88  to the first end  86 . 
     The middle portion  64  of the hull  40  may include a flattened keel  44 B having a width that increases from the fore portion  92  to the aft portion  94  of the middle portion  64 . The flattened keel  44 B may have a deadrise angle of 0°. As a non-limiting example, the width of the flattened keel  44 B at the aft portion  94  of the middle portion  64  may be between approximately 2% and approximately 25% greater than the width of the flattened keel  44 B at the fore portion  92  of the middle portion  64 . Like the bow portion  62 , the middle portion  64  of the hull  40  may include a plurality of strakes  80  protruding from the deadrise portion  46  of the hull bottom  44 . As a non-limiting example, six strakes  80  are shown in  FIGS. 4-11 . The keel  44  and a deadrise portion  46  on either side of the keel  44  may be disposed between the two innermost strakes  80 , forming a keel ridge  95  between the two innermost strakes  80 . Each of the outermost strakes  80  may define the chine  58  between the deadrise portions  46  and the sidewalls  60 . The first end  96  of each strake  80  may be located just aftward of the first transverse air channel  74  and the second end  98  of each strake  80  may be located just forward of the second transverse air channel  76 . The first end  96  of each strake  80  may be gradually tapered or flattened to meet the rear edge of the first transverse air channel  74 , which may reduce the resistance of the first end  96  as it hits the oncoming water. Each strake  80  may be parallel to the centerline  70  of the hull  40 . Unlike the bow portion  62 , the strakes  80  of the middle portion  64  may not have a tapered shape, and the width of each strake may be continuous from the first end  96  to the second end  98 , and may be the same or substantially the same as the width of the second end  88  of the corresponding bow portion strake  78 . 
     Unlike the bow  62  and middle  64  portions of the hull  40 , the stern portion  66  may not include a keel ridge  95  between the two innermost strakes  82 . Instead, the stern portion  66  may include a longitudinal flattened area  100  disposed between the two innermost strakes  82 A. As shown, for example, in  FIGS. 1 and 8 , the boundaries of the longitudinal flattened area  100  are defined by the two innermost strakes  82 , the second transverse air channel  76 , and a ledge  102  in the stern portion  66 . 
     The strakes  82  of the stern portion  66  may protrude from the deadrise portion  46  of the hull bottom  44 . Further, the two innermost strakes  82 A may be offset toward the centerline  70  from the two innermost strakes  78 ,  80  of the bow portion  62  and the middle portion  64 , respectively. The ledge  102  may lead to a recessed area  104  in the stern portion  66  adjacent to the transom  68 . As a non-limiting example, six strakes  82  are shown in  FIGS. 4-11 . The outermost strakes  82 C may define the chine  58  between the deadrise portions  46  and the sidewalls  60 . The first end  106  of each strake  82  may be located just aftward of the second transverse air channel  76  and the second end  108  of each strake  82  may be located just forward of the ledge  102 . The first end  106  of each strake  82  may be gradually tapered or flattened to meet the rear edge of the second transverse air channel  76 , which may reduce the resistance of the first end  106  as it hits the oncoming water. Each strake  82  may be parallel to the centerline  70  of the hull  40 . Like the middle portion  64 , the strakes  82  of the stern portion  66  may not have a tapered shape, and the width of each strake  82  may be continuous from the first end  106  to the second end  108 , and may be the same or substantially the same as the width of the second end  98  of the corresponding middle portion strake  80 . The recessed area  104  of the stern portion  66  may not include any strakes but may include a flattened keel ridge  95 . 
     As is best seen in  FIGS. 8A and 8B , each strake  82  in the stern portion  66  may define an outer lateral surface  110 , an inner lateral surface  112 , and a face  114 . The terms “outer” and “inner” may be used with reference to the centerline  70 , with the inner lateral surface  112  of each strake  82  being closest to the centerline  70 . In the two outermost strakes  82 C, the outer lateral surface  112 A may be integrated with at least a portion of the sidewall  60 . Explained in another way, the sidewalls  60  of the hull  40  may define at least a portion of the outer lateral surface  112 A of each of the outermost strakes  82 C. 
     The face  114  of each strake  82  in the stern  66  portion of the hull  40  may be parallel or substantially parallel to, although not coplanar with, the flattened keel  44 B. In other words, the face  114  of each strake  80 ,  82  may have a 0° deadrise. The outer  110  and inner  112  lateral surfaces of these strakes  80 ,  82  may be substantially orthogonal to the face  114 . That is, the outer  110  and inner  112  lateral surfaces may meet the face  114  at an angle that is 85° (±10°). The angle at which the outer  110  or inner  112  lateral surface meets the deadrise portion  46  of the hull bottom  44  may depend on the deadrise angle of the hull bottom  44  at the meeting point. Generally, the term “deadrise angle” may refer to the angle formed between horizontal and the hull at any given point. 
     Each strake  78 ,  80  in the bow portion  62  and the middle portion  64  may define an outer lateral surface  110  and a face  114  that connects to the deadrise portion  46  without defining a face  114  that has a 0° deadrise and an inner lateral surface that is substantially orthogonal to the face. Instead, the face  114  of the strakes  78 ,  80  may itself have deadrise angle that is in the opposite direction to the deadrise  46  of the hull bottom  42 . Optionally, there may be a slight depression between the face  114  and the deadrise  46 , which could be considered to be an inner surface  112 . Alternatively, the strakes  78 ,  80  may be configured similar to the strakes  82  in the stern portion  66  of the hull. In either configuration, the face  114  of each strake  78  in the bow portion  62  of the hull  40  may be tapered from the second end  88  to the first end  86  of the strake  78 . So, from the first end  86  of the strake to a distance aftward from the first end  86 , the strake may include a sharp ridge and not a planar face. 
     Continuing to refer to  FIGS. 4-11 , the hull  40  may include a first transverse air channel  74  and a second transverse air channel  76 , each being incorporated into a step  72 . Each air channel  74 ,  76  may extend from the port-side chine  58  to the starboard-side chine  58 , and may include an air inlet  116  on either end (for example, as shown in  FIG. 5 ). Although referred to as “transverse” steps  72  and air channels  74 ,  76 , this term may be used in the sense that the steps  72  and air channels  74 ,  76  transverse the centerline  70  of the hull  40 . However, it will be understood that these features may not be entirely orthogonal to the centerline  70 , and may instead be slightly V-shaped, with either side of the centerline being directed aftward, forward, or having another configuration for optimizing air intake and retention. The air channels  74 ,  76  may divide the hull bottom  42  into three planing surfaces, one being in the bow portion  62 , a second being in the middle portion  64 , and a third being in the stern portion  66 . 
     As shown in the cross-sectional view of  FIG. 6 , each air channel may be a recessed area within the hull bottom  44  that is defined by a ceiling  120 , fore wall  122 , and an aft wall  124 . The fore  122  and aft  124  walls may be orthogonal to or substantially orthogonal to the ceiling  120 . That is, the fore  122  and aft  124  walls may meet the ceiling  120  at angles that are within 85°±10°. Alternatively, the fore  122  and/or aft wall  124  may each meet the ceiling  120  at any angle that defines an air channel that effectively traps atmospheric air within and prevents the trapped air from flowing longitudinally over the hull bottom  44  from the air channel  74 ,  76  toward the transom (i.e. sternward). Each air inlet  116  may include a flow separator  118 , the configuration of which causes water on the sidewalls  60  of the watercraft adjacent to the inlet  116  to flow away from the hull  40 . This may reduce the amount of water that flows into each air channel  74 ,  76  and may help retain the atmospheric air within the channel  74 ,  76 . Preventing water from entering the air channels  74 ,  76 , and resulting wetting of the channel  74 ,  76 , may prevent an increase in resistance and, therefore, reduction in efficiency. 
     Referring particularly now to  FIG. 10 , a bottom view of a stylized representation of the bottom of the improved stepped hull is shown, with the flow of air and water over the hull bottom being depicted by arrows. As the watercraft moves forward initially from a stop, a slight vacuum is created in the air channels, which causes atmospheric air to be sucked into the air channels  74 ,  76  through the air channel inlets  116 . This air is then retained within the air channels  74 ,  76  as the boat&#39;s speed increases, the configuration of which channels  74 ,  76  prevents the air from flowing longitudinally along the hull bottom  44  toward the transom  68 . The air within the air channels  74 ,  76  is shown in solid arrows in  FIG. 10 . Likewise, the flow of water over the retained air within the air channels  74 ,  76  and the hull bottom  44  is shown in dashed arrows in  FIG. 10 . The flow of water may be directed between the longitudinal protruding strakes  78 ,  80 ,  82 , which may increase efficiency. 
     Referring now to  FIG. 11 , a cross-sectional view of the stern portion of an improved stepped hull is shown during a turning maneuver. During a turn, the strakes  78 ,  80 ,  82  (strakes  80  are shown in  FIG. 11 ) generate high pressure transversely to the fore-and-aft line of the watercraft (that is, athwartships) to resist yawing and side velocity, holding the stern portion  66  of the watercraft in the turn and preventing the watercraft from spinning about its center point during a turn. An exemplary water line  126  is shown in dashed lines for reference. 
     Referring now to  FIGS. 12 and 13 , a watercraft having a stepped hull  130  known in the art and the improved stepped hull in accordance with the present invention are each shown during a turning maneuver. Positions  130 A,  130 B,  130 C,  130 D are stylized representations of the watercraft in various positions when effectuating, for example, an approximately 90° turn. Stepped hulls known in the art may be designed to allow air from the steps  30  and/or air channels  32  to flow aftward, that is, toward the transom  26 . This air may create lift and reduce the friction between the hull and the water. Although this reduction in wetted hull surface may make the watercraft faster and more efficient, it may also cause the stern portion  66  to become “slippery,” which can lead to handling, stability, and maneuverability difficulties. Essentially, the stern portion  66  of the watercraft may slide across the water in a wider arc than the bow portion  64 , as shown in  FIG. 12 . 
     In contrast, a watercraft having an improved stepped hull design  134  may follow the turn without the stern portion  66  sliding out from the bow portion  64 . Positions  136 A,  136 B,  136 C,  136 D are stylized representations of the watercraft in various positions when effectuating, for example, an approximately 90° turn. Unlike the stepped hull of the prior art, the portions of the improved stepped hull bottom  44  between the transverse air channels  74 ,  76  remain in contact with the water, preventing uncontrolled sideways movement of the stern portion  66 . This may be best shown in the comparison between the hull position of  FIGS. 12 and 13 . In  FIG. 12 , the stern portion  66  of the watercraft  130  in positions  132 B and  132 C is not tracking the bow portion  64  along the turn. Rather, the stern portion  66  is sliding out from the bow portion  64 . In contrast, the stern portion  66  of the watercraft  134  in positions  136 B and  136 C in  FIG. 13  follows the bow portion  64  through the turn. 
     It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described herein above. In addition, unless mention was made above to the contrary, it should be noted that all of the accompanying drawings are not to scale. A variety of modifications and variations are possible in light of the above teachings without departing from the scope and spirit of the invention, which is limited only by the following claims.