Abstract:
A drag-reducing air chamber is formed under a watercraft when the watercraft is underway. Air enters into the air chamber when the watercraft is moving forward. Supplemental air is introduced into the air chamber by an air scoop mounted to the bow in a first embodiment and in side-mounted air scoops in another embodiment. A one-way valve in an air passageway between the air scoop and the air chamber prevents air from flowing from the air chamber to the air scoop. A pair of elongate rails depends from opposite sides of the hull and defines the sides of the air chamber. Shorter rails may be used in high-speed applications where the bow of the watercraft is lifted from the water.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates, generally, to watercraft. More particularly, it relates to a watercraft design that directs an airflow under the hull to reduce drag. 
   2. Description of the Prior Art 
   A Carolina skiff is a small fishing boat having a pair of rails that extend substantially the entire length of the boat. A first rail depends from the port side of the hull and a second rail depends from the starboard side thereof. The rails help keep the watercraft traveling in a straight line when the watercraft is traveling at normal speeds. 
   If a Carolina skiff, or similar watercraft, is operated at high speeds, the bow lifts out of the water. Accordingly, the respective leading ends of the rails are also lifted from the water. 
   Thus there is a need for a Carolina skiff designed for high speed operation. 
   When a Carolina skiff, or similar watercraft, is operating at high speeds, it is subjected to considerable drag. This increases the fuel consumption rate of the motor. 
   There is a need, therefore, for a watercraft design that enables a watercraft like a Carolina skiff to travel at high rates of speed with a reduced drag and thus a reduced rate of fuel consumption vis a vis the Carolina skiff of the prior art. 
   Earlier inventions generally in this field of technology are disclosed in U.S. Pat. Nos. 3,742,888 and 3,688,724, 3,518,956, and Great Britain patent No. 1,001,059. 
   However, in view of the prior art considered as a whole at the time the present invention was made, it was not obvious to those of ordinary skill in the pertinent art how the known Carolina skiffs and similar watercrafts could be modified to further reduce drag and increase speed. 
   SUMMARY OF THE INVENTION 
   The long-standing but heretofore unfulfilled need for a Carolina skiff or similar watercraft having reduced drag so that it is capable of relatively high speed travel when under its own power and requiring reduced power to tow it is now met by a new, useful, and nonobvious invention. 
   The novel watercraft of this invention includes a bow, a stern, a deck and a hull. An air chamber defined at its top by the rigid hull, at its sides by the rails that depend from opposite sides of the hull, and at its bottom by the body of water that buoyantly supports the watercraft. 
   More particularly, the air chamber has a forward end near the bow and a rearward end somewhat forwardly of the stern so that air flows into the air chamber at the forward end and so that air flows out of the air chamber under the stern as the watercraft undergoes forward travel. 
   Air in the air chamber reduces the drag of the watercraft, thereby enabling the watercraft to travel faster under its own power and reducing the power required to drag a small watercraft behind a larger watercraft. 
   Air produces less drag than water. Accordingly, replacing water with low-density air reduces the wetted surface area of the hull and therefore reduces drag. However, unlike some earlier designs, the air in the air chamber does not form a relatively static bubble beneath the watercraft that expands and contracts in size as waves form troughs and crests, respectively. In contrast, air enters into and exits the air chamber at substantially the speed at which the watercraft is traveling. 
   When the watercraft is under way, air enters into the air chamber. Since air density is about one-eight hundredth ( 1/800th) the density of water, the drag developed by the watercraft is substantially reduced. 
   Significantly, the reduction in drag is beneficial when the watercraft is under tow as well. In some cases, the watercraft could ride in the wake of a larger, towing craft and the drag could be reduced to a very low value. 
   Thus it is understood that the primary reduction in drag is achieved by the air chamber formed by the hull of the watercraft and the side rails that depend from the hull on opposite sides of the watercraft. 
   At speeds above a certain threshold, such as fifteen (15) knots, the drag may be further reduced by the provision of an air scoop mounted to the bow. 
   In a preferred embodiment, the air scoop is made of fiberglass formed integrally with the fiberglass that forms the watercraft. The air scoop is adapted to collect air when the watercraft is undergoing forward travel and to direct air into the air chamber. The air scoop has a generally elliptical shape such that a transverse extent thereof is greater than a height extent thereof. 
   When the watercraft is undergoing forward travel, air enters into the air scoop and is directed into the air chamber. Air entering into the air chamber reduces the drag against forward travel as aforesaid. Air in the air chamber escapes the air chamber by flowing under the stern so that an airflow is established into and out of the air chamber as the watercraft undergoes forward travel. 
   A stern plate is positioned rearwardly of the air chamber and is tilted at a slight angle relative to horizontal with its leading edge a little higher than its trailing edge. Air exiting the air chamber thus is constrained to flow under the stern plate. This raises the stern of the watercraft slightly and further reduces drag. 
   An airflow passageway extends from a leading end of the air scoop into the air chamber. The airflow passageway may have a gradual reduction of volume as it approaches the air chamber or the airflow passageway may have a constant volume. 
   Air pressure in the air chamber is lower than atmospheric air pressure so that air is drawn or rammed into the air scoop when the watercraft is undergoing forward motion (whether under its own propulsion or due to towing). 
   A one-way valve is mounted in the airflow passageway to enable ram airflow into the air chamber when the watercraft is in forward motion and to prevent reverse direction airflow so that ram air flowing in the airflow passageway toward the air chamber cannot flow in an opposite direction. 
   Thus, air in the air chamber does not flow toward the air scoop when the bow of the watercraft is momentarily lifted from the water when the watercraft is traveling in choppy waters. 
   The one-way valve may be provided in many forms, all of which are within the scope of this invention. 
   In a preferred embodiment of the one-way valve, an impervious-to-air gate is hingedly mounted to an upper wall of the air passageway. The gate swings open about its hinges when ram air flows from the air scoop to the air chamber. The gate closes under its own weight when air attempts to flow from the air chamber toward the air scoop. 
   An important object of this invention is to provide a watercraft that travels substantially faster than a conventional watercraft when the power inputs are equal. 
   A more specific object is to provide a watercraft that travels faster than conventional watercraft due to a reduced drag design. 
   Another object is to provide a watercraft having reduced drag so that is easier to tow than a conventional watercraft. 
   These and other important objects, advantages, and features of the invention will become clear as this description proceeds. 
   The invention accordingly comprises the features of construction, combination of elements, and arrangement of parts that will be exemplified in the description set forth hereinafter 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 objects of the invention, reference should be made to the following detailed description, taken in connection with the accompanying drawings, in which: 
       FIG. 1  is a front perspective view of the novel watercraft; 
       FIG. 2  is a side elevational view thereof; 
       FIG. 3A  is a side elevational view in longitudinal section of a forward half of the novel watercraft; 
       FIG. 3B  is an exploded view of the circled part of  FIG. 3A  denoted  3 B; 
       FIG. 4  is a bottom plan view of the novel watercraft; 
       FIG. 5  is a sectional view taken along line  5 — 5  in  FIG. 4 ; 
       FIG. 6  is a side elevational view of a second embodiment; 
       FIG. 7  is a front perspective view of a third embodiment; 
       FIG. 8  is a bottom plan view of said third embodiment; 
       FIG. 9  is a rear elevational view of said third embodiment; 
       FIG. 10  is a rear perspective view of a dinghy that incorporates the inventive parts; 
       FIG. 11  is a top plan view of the dinghy depicted in  FIG. 10 ; 
       FIG. 12  is a transverse sectional view taken along line  12 — 12  in  FIG. 10 ; and 
       FIG. 13  is a longitudinal sectional view taken along line  13 — 13  in  FIG. 11 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring now to  FIGS. 1 and 2 , it will there be seen that the reference numeral  10  denotes a first embodiment of the novel watercraft as a whole. The invention will be described by making reference to a Carolina Skiff® watercraft for convenience purposes, but the teachings and suggestions of this disclosure are also applicable to other small craft such as yachts, RIBs (rigid inflatable boats), dinghies, rowboats, motorboats, surfboards, windsurfing boards, and the like. The teachings and suggestions of this invention are equally applicable to large craft. 
   Watercraft  10  includes bow  12 , hull  14 , first sidewall  16 , a second sidewall that is not depicted, an operator&#39;s station  18 , motor  20 , stern  22 , and transom  24 . 
   A first elongate rail  26  depends from a first side of hull  14  and a second elongate rail  28  ( FIGS. 5 ,  7  and  9 ) depends from a second side of said hull  14 . 
   Air intake scoop  30  is formed integrally with bow  12 . Air intake scoop  30  has a generally elliptical configuration so that its transverse extent exceeds its height extent. 
     FIGS. 3A and 3B  depict air chamber  32  having a top defined by hull  14  and sides defined by said elongate, parallel rails  26 ,  28 . 
   The width of air intake scoop  30  is about the same as the width of air chamber  32 , thereby ensuring that the volume of air entering into said air chamber per unit of time is a large volume. 
   It should be understood that air scoop  30  is not required to provide the reduced drag effects offered by air chamber  32 . At relatively slow speeds, sufficient air enters into air chamber  32  to provide the drag reduction needed. At higher speeds, supplemental air from air scoop  30  becomes beneficial at maintaining the air in said air chamber. 
   Air scoop  30  includes an airflow passageway, denoted  36  generally in  FIGS. 3A and 3B , that extends from the leading edge of air scoop  30  to the leading end of air chamber  32 . 
   As depicted in  FIGS. 4 and 5 , airflow passageway  36  maintains a constant width along its longitudinal extent from scoop  30  to air chamber  32 . However, its vertical extent gradually decreases as it approaches air chamber  32  as best depicted in  FIGS. 3A and 3B . 
   A more abrupt reduction in height is provided by downwardly extending constriction member  38  at the trailing end of air passageway  36 . 
   Flap  40  is hingedly mounted to the trailing end of constriction member  38 . Flap  40  has a position of repose depicted in dotted lines in  FIG. 3B . When watercraft  10  is underway, air flowing into air passageway  36  lifts flap  40  to its fully open  FIG. 3B  solid line position  40 . An amount of opening between the fully closed and fully open positions may also occur at some speeds. 
   The volume of air chamber  32  is greater then the volume of the constriction caused by constriction member  38 . Thus, the air pressure within air chamber  32  is less than atmospheric pressure, thereby drawing ambient air into air scoop  30  as watercraft  10  travels forwardly. 
     FIG. 6  depicts a second embodiment where an air chamber  32  is formed in hull  14 . Thus, this embodiment requires substantial modification of a Carolina Skiff. 
     FIGS. 7–9  depict a third embodiment where air scoops having leading ends  30   a ,  30   b  and trailing ends  31   a ,  31   b , respectively, are formed in the sides of the watercraft. The respective trailing ends  31   a ,  31   b  of said air scoops are positioned rearwardly of bow  14  and slightly forwardly of stern  22  of watercraft  10 , between elongate rails  26 ,  28 . This is due to the fact that at high speeds, the bow of the watercraft lifts from the water and only the stern area of the watercraft is in contact with the water. Accordingly, air from air scoops  30   a  and  30   b  is introduced into the stern end of air chamber  32 . Such air is constrained to flow out from under the stern end of the watercraft because rails  26 ,  28  prevent lateral flow thereof. 
   It should be noted that rails  26 ,  28  need not extend very far forwardly of stern  22  in watercraft intended for high speed travel. 
   A constriction member such as constriction member  38  of the first embodiment, together with flap  40 , may be provided at the respective trailing ends  31   a ,  31   b  of air scoops  30   a ,  30   b  to prevent reverse airflow as in the first embodiment. 
   A dinghy  10   a  equipped with the novel air chamber is depicted in  FIGS. 10–13 . Rails  26 ,  28  are added to the hull of the dinghy to frame the longitudinally-extending sides of air chamber  32 . The construction of air chamber  32  is disclosed in co-pending U.S. patent application filed Dec. 23, 2003, bearing Ser. No. 10/707,590, and having the same title as the present disclosure, which disclosure is incorporated herein by reference. 
     FIG. 10  depicts air scoop  30  at the bow of dinghy  10   a  and  FIG. 11  depicts how air passageway  36  extends from said air scoop to the leading end of air chamber  32 .  FIG. 11  further depicts constriction member  38  at the leading end of air chamber  32  and transom  24  that forms a barrier at the trailing end of said air chamber. 
   As is clear from  FIG. 12 , elongate rails  26 ,  28  may be added to virtually any watercraft. Dinghy  10   a  is depicted just to point out this important aspect of the invention. The effect of air chamber  32  is greater in a dinghy because, as pointed out in the incorporated disclosure, the flexible bottom of a dinghy makes it easy to form a large air chamber therein. In rigid hull watercraft, the best way to create an air chamber beneath the hull is to use rails such as rails  26 ,  28 , as disclosed herein, to prevent air under the hull from escaping laterally. 
   The effect of air flowing through air chamber  32  is to reduce drag because the above water surfaces of air chamber  32  are contacted primarily by air flowing therepast, not primarily by water. 
   When a conventional watercraft is in operation, a pair of bow waves are formed that extend rearwardly from the watercraft in an inverted “V” shape, i.e., a first bow wave will form on the port side of the watercraft and a second bow wave will form on the starboard side. These bow waves include spray and thus are white-in-color, like the white-in-color water produced by a waterfall. At night, an unlit conventional watercraft may be hard to see but night vision goggles will enable a user to see the spray caused by the bow waves. An important effect of the novel design is to suppress bow waves. A watercraft that incorporates the teachings and suggestions of this disclosure is a stealthy watercraft to the extent that it operates at high speeds yet does not produces detectable bow waves, even if night vision goggles are used. 
   The stern wake, made up of white-in-color bubbles that are also detectable in darkness with the aid of night vision goggles, may also be suppressed to the point where it cannot be detected by such equipment. Motor  20  is moved away from the stern, toward the bow so that the white water created by the propellers is substantially bubble-free by the time it flows under the stern and becomes the stern wake. Empirical studies will suggest the ideal mounting for watercraft of differing lengths and speeds. A fast watercraft will require a long distance between the propellers and the stern to increase the dwell time of the bubbles under the hull so that the bubbles are gone or substantially gone by the time the stern of the watercraft passes over them. A shorter distance will be satisfactory for a watercraft that travels at slower speeds. 
   Accordingly, the combination of a mid or forward-mounted motor to suppress the stern wake, together with the novel structure disclosed herein to suppress bow waves, produces a watercraft that moves with a high degree of stealth at night even if night vision goggles are employed in an effort to see it. 
   It will thus be seen that the objects set forth above, and those made apparent from the foregoing description, are efficiently attained. Since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matters contained in the foregoing 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 following claims 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 that, as a matter of language, might be said to fall therebetween. 
   Now that the invention has been described,