Abstract:
A hydrodynamic device for use with a recreational water vessel such as a surfboard, disrupts a flow of water under the recreational water vessel. A channel member ( 12 ) and a fixing device ( 14 ) are attachable to an underside of the recreational water vessel. The fixing device ( 14 ) may have lugs ( 44 ) arranged to be received in corresponding recesses in the underside of the vessel. Water flowing between the underside of the vessel and the channel member ( 12 ) passes from a high water-pressure zone to a low water-pressure zone, which enhances forward thrust of the recreational water vessel in the water.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a hydrodynamic device, in particular for use with water vessels. 
     BACKGROUND OF THE INVENTION 
     Most recreational water vessels, such as surfboards, bodyboards, windsurfers and the like rely on at least one fin attached to an underside of the water vessel to provide stability to the water vessel when it is in use. Developments in the shape and structure of such fins have gradually improved the performance of these vessels, but few fin designs have enhanced the thrust and turning or steering ability of these vessels in the water. 
     The present invention seeks to overcome at least some of the aforementioned disadvantages. 
     SUMMARY OF THE PRESENT INVENTION 
     In accordance with one aspect of the present invention there is provided a hydrodynamic device for use with a water vessel, comprising a channel member for disrupting a flow of water under the water vessel, the channel member being arranged, in use, to be fixed to an underside of the water vessel with an attachment means, wherein water flowing between the underside of the vessel and the channel member passes from a high water pressure zone to a low water pressure zone thereby enhancing a forward thrust of the water vessel in the water. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
     FIG. 1 is a perspective view of a hydrodynamic device in accordance with the present invention; 
     FIG. 2 is a side elevatory view of the hydrodynamic device shown in FIG. 1; 
     FIG. 3 is a plan view of the hydrodynamic device shown in FIGS. 1 and 2; 
     FIG. 4 is a front view of the hydrodynamic device shown in FIGS. 1,  2  and  3 ; 
     FIG. 5 is a perspective view of a further embodiment of a hydrodynamic device shown in accordance with the present invention; 
     FIG. 6 is a side elevatory view of the hydrodynamic device shown in FIG. 5; 
     FIG. 7 is a plan view of the hydrodynamic device shown in FIGS. 5 and 6; and 
     FIG. 8 is a front view of the hydrodynamic device shown in FIGS. 5,  6  and  7 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In FIGS. 1-8 of the accompanying Figures, there is shown a hydrodynamic device  10 . The hydrodynamic device  10  is arranged, in use, to be fixed to an underside of a water vessel. In particular, the hydrodynamic device  10  is arranged, in use, to be fixed to the underside of recreational water vessels, preferably surfboards, bodyboards, windsurfers and the like. It is envisaged that the hydrodynamic device  10  will replace a conventional fin on the water vessel. 
     The hydrodynamic device  10  includes a substantially U-shaped channel member  12  and an attachment means  14  for fixing the channel member  12  to the underside of the vessel. The channel member  12  is longitudinally aligned with and equidistantly spaced from opposing sides of the vessel. The channel member  12  is fixed at any point, including and between, a first point disposed substantially equidistantly spaced from a front end and a rear end of the underside of the vessel and a second point disposed adjacent to the rear end of the underside of the vessel. 
     The U-shaped channel member  12  includes a pair of opposing side walls  20  and a lower wall  30  interconnecting with, and spanning, a lower portion  22  of each side wall  20  Preferably, the side walls  20  and the lower wall  30  are cambered. 
     As shown in FIGS. 2 and 6, each side wall  20  has a fin-like profile The side wall  20  has an upper side  26  disposed parallel with a lower side  24 . However, a foremost portion  21  of the upper side  26  extends further forward than a foremost portion  25  of the lower side  24 , such that a front side  28  of the side wall  20  is rearwardly and downwardly inclined. Preferably, the front side  28  is slightly convex A front surface  29  of the side wall  20  tapers slightly towards the lower portion  22  of the side wall  20 . A rear side  82  of the side wall  20  is provided with a first convex portion  62  disposed adjacent to a rearmost portion  27  of the lower side  24 , a second convex portion  64  disposed adjacent to a rearmost portion  23  of the upper side  26 , and a concave portion  66  disposed intermediate the first and second convex portions  62 ,  64  The rearmost portion  23  of the upper side  26  extends further rearward than the rearmost portion  27  of the lower side  24 , such that the rearmost portion  23  overhangs the lower wall  30 , as shown in FIGS. 2,  3 ,  6  and  7   
     It can also be seen from FIGS. 3,  4 ,  7  and  8  that the foremost portions  21 ,  25 , and in particular the foremost portion  21  of the upper side  22 , are curved slightly inwardly towards the corresponding foremost portions  21 ,  25  of the opposing side wall  20 . In this way, a front opening  18  of the channel member  12  is narrower than a rear opening  19  of the channel member  12   
     Although the lower wall  30  of the channel member  12  is substantially rectangular, it will be evident from FIGS. 1,  3 ,  5  and  7  that a front side  32  of the lower wall  30  is slightly concave Furthermore, an upper surface  34  of the lower wall  30  overhangs the lower surface  36  of the lower wall  30  at the front side  32  of the lower wall  30 , such that a front surface  38  of the lower wall  30  inclines rearwardly of the upper surface  34   
     The attachment means  14  shown in FIGS. 1-4 comprises a central wall  42  and a plurality of lugs  44  upwardly depending from an upper surface  41  of the central wall  42 . Each lug  44  is arranged, in use, to be received in a corresponding recess (not shown) disposed in the underside of the water vessel. 
     A lower surface  43  of the central wall  42  is integral with the lower wall  30  of the channel member  12 . The central wall  42  is disposed substantially parallel with and equidistantly spaced from the side walls  20  of the channel member  12 . A front portion  45  of the central wall  42  projects increasingly forwardly from the lower wall  30 , as shown in FIGS. 1 and 3, such that a front surface  47  of the front portion  45  is upwardly curved and overhangs the lower wall  30  The front surface  47  is also tapered to a sharp outwardly extending front edge  49  Opposing surfaces  48  of the central wall  42  are slightly convex and taper slightly from the upper surface  41  to the lower surface  43  of the central wall  42 . 
     The hydrodynamic device  10  shown in FIGS. 5-8 is not provided with a central wall  42  and a plurality of lugs  44  to fix the device  10  to the underside of a vessel Instead, the device is fixed to the underside of the vessel in a desired location by applying a resin mixture to the upper surfaces  33  of the side walls  20  by known means such that the channel member  12  becomes “glassed-on” to the underside of the vessel. 
     It will be understood that the attachment means may also comprise a snap-lock fitting device, an adhesive or any other known conventional means by which a fin may be attached to the underside of the vessel in the desired location. 
     Referring to FIGS. 5-8, the channel member  12  is provided with a harmonic damper  16  for dampening vibrations which disrupt the performance of the water vessel in the water. The harmonic damper  16  includes two opposing ribs  52  longitudinally disposed on the upper surface  34  of the lower wall  30 . A foremost portion  54  of the ribs  52  protrude forwardly from the front side  32  of the lower wall  30 . 
     The harmonic damper  16  also includes a curved member  56  disposed between the ribs  52  and adjacent to the front side  32  of the lower wall  30  Preferably, the curved member  56  is attached to the lower surface  36  of the lower wall  30  It is envisaged that the curved member  56  will have a very thin thickness, and thus the curved member  56  will be only slightly raised from the lower surface  36 . 
     It is envisaged that the hydrodynamic device  10  will be formed from a low friction material, preferably selected from a group including but not limited to acrylic, glass, carbonite, polyurethane, plastics, nylon, carbon fibre, teflon, and synthetic skin. 
     It is also envisaged that the hydrodynamic device weighs between 80 g-150 g. 
     Preferably an outer surface of the hydrodynamic device  10 , comprising the lower surface  36  of the lower wall  30  and the respective outer surfaces of the side walls  20 , is a polished surface. 
     Preferably, an inner surface of the hydrodynamic device  10 , comprising the upper surface  34  of the lower wall  30 , the respective inner surfaces of the side walls  20 , and the opposing surfaces  48  of the central wall  42 , is a matte surface However, it is envisaged that the inner surface may also be a polished surface. 
     In use, the hydrodynamic device  10  is fixed to the underside of water vessel by engaging the lugs  44  depending from central wall  42  in corresponding recesses located in the vessel. Alternatively, the upper surfaces  23  of the side walls  20  of the channel member  12  may be “glassed on” to said underside. It is envisaged that any one of several known attachment means may be adapted to fix the device  10  to the desired location on the vessel. 
     The device  10  becomes submerged in water when the underside of the vessel partially submerged in, or is disposed on the surface of, a body of water. 
     A portion of water moving relative to the inner surface of the channel member  12  will pass through a high pressure zone as it enters the front opening  18  of the channel member  12 . The high pressure zone is located adjacent to the front surfaces  29  of the side walls  20  and the front surface  38  of the lower wall  30 . 
     Similarly, that same portion of the channel member  12  will pass through a low pressure zone as it exits the rear opening  19  of the channel member  12 . The low pressure zone is located adjacent the inwardly curved portions  66  of the rear sides  82  of the side walls  20 . 
     The combined effect of the high pressure zone and the low pressure zone located at respective front and rear openings  18 ,  19  in the channel member  12 , and the cambered side walls  20  and the cambered lower wall  30 , is to exert decreasing pressure on the portion of water moving from the front to the rear openings  18 ,  19  of the channel member  12  relative to the device  10 . Water enclosed between the device  10  and the underside of the vessel thus behaves as if it is moving in an expansion chamber, resulting in production of water turbulence and thereby the production of forward thrust to the vessel. 
     Modifications and variations as would be apparent to a skilled addressee are deemed to be within the scope of the present invention.