Abstract:
A prop wash straightening apparatus for increasing the efficiency of propeller-driven watercraft. An elongated outer tubular member open at each end thereof is adapted for connection to the boat or vessel to position said outer member immediately downstream of the propeller and in substantially longitudinal fixed alignment with the direction of axial thrust produced by the propeller. A plurality of elongated hollow open-ended inner tubular members are positioned in closely packed fashion within, and generally coextensive with a substantial portion of the length of the outer tubular member. A proximal or forwardly end of the inner tubular members is positioned in close proximity to a trailing plane of the propeller. The outer tubular member extends from the proximal end of the inner tubular members to surround the blade tips of the propeller to direct substantially all prop wash from the propeller into the inner tubular members.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   Not applicable 
   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   Not applicable 
   INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC 
   Not applicable 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates generally to propeller propulsion systems for watercraft and more particularly to thrust enhancing devices and apparatus for improving the efficiency of such propeller propulsion means. 
   2. Description of Related Art 
   The use of a multi-bladed propeller to propel a watercraft, boat or vessel through the water is ancient. Although other propulsion means have been developed in recent times, the twisted blade propeller remains the mainstay of water propulsion. Although propeller configuration and design have become extremely sophisticated through the use of computerized design techniques, nonetheless as a propeller rotates in water to produce a net axial flow of water which propels the watercraft in the opposite direction thereto, some of the water discharging as prop wash from the propeller does so from the tips at an acute angle of up to 90° to the axial flow or longitudinal axis of the propeller. This nonaxial water flow off the tips of the propeller leads to considerable loss in efficiency and thrust for which the propeller is capable of producing. Moreover, a spiral twist is introduced into the water flow by the propeller which also dissipates or reduces some of the axial thrust potential of the propeller. 
   A number of prior art devices have attempted to improve the efficiency of water flow produced by propulsion means including these conventional propellers as follows: 
   U.S. Pat. No. 2,803,211 to Erlbacher 
   U.S. Pat. No. 3,249,083 to Irgens 
   U.S. Pat. No. 3,528,382 to Clark 
   U.S. Pat. No. 3,722,454 to Silvester 
   U.S. Pat. No. 3,934,538 to Canazzi 
   U.S. Pat. No. 4,046,097 to Hornung 
   U.S. Pat. No. 4,505,684 to Holden, et al. 
   U.S. Pat. No. 4,637,801 to Schultz 
   U.S. Pat. No. 5,651,707 to Lemont 
   U.S. Pat. No. 5,906,522 to Hooper 
   In particular, U.S. Pat. No. 3,528,382 invented by Clark, et al. discloses a propulsive system which will utilize a considerable amount of energy from the rotation of the screw race by restoring it as for and aft propulsive effort on the vessel. A propeller duct assembly for watercraft which enhances the thrust of the propeller is taught by Schultz in U.S. Pat. No. 4,637,801. 
   U.S. Pat. No. 5,906,522 invented by Hooper discloses a thrust enhancer for a marine propeller. Irgens, in U.S. Pat. No. 3,249,083 teaches marine propulsion units including reaction jet arrangements for developing thrust. 
   A driving mechanism for watercraft which utilizes the propeller wash to impart additional driving thrust to the vessel is taught by Masta in U.S. Pat. No. 2,884,890 and Lemont teaches a propulsive thrust ring system in U.S. Pat. No. 5,651,707. 
   U.S. Pat. No. 3,722,454 to Silvester discloses a thrust augmenter device and Holden, et al. discloses a thrust tube propulsion system in U.S. Pat. No. 4,505,684. 
   The present invention provides an economical easily attachable addition to virtually any watercraft which is propeller driven. The apparatus forces virtually all of the water discharging from the propeller into an axial flow which discharges there from to produce propulsion for the watercraft in a substantially rearwardly axial flow without substantial amounts of radial or spiral twist prop wash energy loss. 
   BRIEF SUMMARY OF THE INVENTION 
   This invention is directed to a prop wash straightening apparatus for increasing the efficiency of propeller-driven watercraft. An elongated outer tubular member open at each end thereof is adapted for connection to the boat or vessel to position said outer member immediately downstream of the propeller and in substantially longitudinal fixed alignment with the direction of axial thrust produced by the propeller. A plurality of elongated hollow open-ended inner tubular members are positioned in closely packed fashion within, and generally coextensive with a substantial portion of the length of the outer tubular member. A proximal or forwardly end of the inner tubular members is positioned in close proximity to a trailing plane of the propeller. The outer tubular member extends from the proximal end of the inner tubular members to surround the blade tips of the propeller to direct substantially all prop wash from the propeller into the inner tubular members. 
   It is therefore an object of this invention to provide a means for increasing the propulsion efficiency of a propeller-driven watercraft. 
   Still another object of this invention is to provide an apparatus for improving the efficiency with which a propeller moves a watercraft in water and which is easily attachable to any propeller-driven watercraft. 
   Yet another object of this invention is to provide an elongated tubular apparatus with inner elongated tubes nested together to force water flow emanating from a propeller in water to transition from a spiral twist into a virtually completely axial flow extending longitudinally rearwardly from the propeller for enhanced efficiency thereof. 
   In accordance with these and other objects which will become apparent hereinafter, the instant invention will now be described with reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
       FIG. 1  is a rear perspective view of one embodiment of the invention attached to a twin propeller-driven watercraft. 
       FIG. 2  is an enlarged broken view of  FIG. 1 . 
       FIG. 3  is a forward perspective view of another embodiment of the invention attached to a steerable lower support unit for the propeller 
       FIG. 4  is a rear perspective view of  FIG. 3 . 
       FIG. 5  is a partially broken view of  FIG. 4 . 
       FIG. 6  is a rear perspective view of the hull of the watercraft incorporating a third embodiment of the invention. 
       FIG. 7  is an enlarged view of a portion of  FIG. 6 . 
       FIG. 8  is a partially broken view of  FIG. 7  from the forwardly perspective view. 
       FIG. 9  is a side elevation section view of still another embodiment of the invention. 
       FIG. 10  is a section view in the direction of arrows  10 — 10  in  FIG. 9 . 
       FIG. 11  is a side elevation section view of still another embodiment of the invention. 
       FIG. 12  is a section view in the direction of arrows  10 — 10  in  FIG. 11 . 
       FIG. 13  is a side elevation section view of still another embodiment of the invention. 
       FIG. 14  is a section view in the direction of arrows  10 — 10  in  FIG. 13 . 
       FIG. 15  is a side elevation section view of still another embodiment of the invention. 
       FIG. 16  is a section view in the direction of arrows  10 — 10  in  FIG. 15 . 
       FIG. 17  is a side elevation section view of still another embodiment of the invention. 
       FIG. 18  is a section view in the direction of arrows  10 — 10  in  FIG. 17 . 
       FIG. 19  is a side elevation section view of still another embodiment of the invention. 
       FIG. 20  is a section view in the direction of arrows  10 — 10  in  FIG. 19 . 
       FIG. 21  is a perspective view of yet another embodiment of the invention. 
       FIG. 22  is a side elevation view of  FIG. 21 . 
       FIG. 23  is a vertical section view taken to the embodiment of the invention of  FIG. 21 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to the drawings, and firstly to  FIGS. 1 and 2 , one embodiment of the invention is there shown generally at numeral  10  connected to the lower transom area of a watercraft A and in the immediate vicinity of and rearwardly extending from each propeller D supported on drive housings B. The apparatus  10  includes a substantially straight open ended outer tubular member  12  having a preferably circular cross section sized only slightly larger than the diameter of the propeller D. Thus tubular member extends from a position surrounding the tips of the propeller and rearwardly thereof. 
   A plurality of inner tubular members  20  are positioned and secured within the outer tubular member  12  and are nested in a most compact or nested orientation which is achievable with respect to circular cross section geometry. The leading surface of this plurality of inner tubular members at  18  is positioned in close proximity to the trailing plane or edge of the propeller D while the rearward planar surface of the inner tubular array at  20  is coplanar with the rearward open end of the outer tubular member  12 . 
   As the propeller D rotates to propel the watercraft A, prop wash is forced fully into the plurality of tubular members  14  in the direction of the arrow shown in hidden lines so that virtually all of the water in the prop wash is resolved into a rearward axial flow within the plurality of inner tubes  14  absent a spiral twist or a radial component to increase propeller efficiency and increase the thrust produced for propelling the watercraft A. 
   Referring now to  FIGS. 3 to 5 , this embodiment  30  of the invention is adapted for attachment to the lower housing E of a steerable propulsion system having propeller G operably connected to the lower unit F for producing horizontal axial thrust in the direction of the arrow in hidden lines within the outer tubular member  32 . The outer tubular member  32  is adapted for attachment by brackets  34  and  36  to the upper and lower portions of the lower unit F such that, as the lower housing E is rotated about an upright steering axis to steer the boat, the apparatus  30  is carried and rotated in the same fashion. 
   In this embodiment  30 , the plurality of inner tubular members  39  is again generally coextensive with and closely nested together within the outer tubular member  32 . However, the outer tubular member  32  extends forwardly of the leading or forwardly surface  41  of the plurality of tubular members  39  so as to surround the tips of the blades of the propeller G to help insure that virtually all of the prop wash discharges through the apparatus  30  in the direction of the hidden arrow in  FIG. 3  absent any spiral twist component shown in phantom at I. Moreover, the plane  38  defining the rearwardly collective surfaces of the plurality of inner tubular members  39  is generally coplanar with the outer tubular member  32  as shown. 
   Referring now to  FIGS. 6 ,  7  and  8 , still another embodiment of the invention is there shown generally at numeral  50  attached in close proximity to a single propulsion means K in alignment with the longitudinal keel J of the watercraft H. A longitudinally extending mounting plate L which drivingly supports the propeller K is utilized to also support the apparatus  50  through its outer tubular member  52 . 
   In this embodiment  50 , the inner tubular members  54  have a hexagonal or honeycombed cross section, the purpose of which is to eliminate the potentially flow inhibiting cross sectional areas positioned between the closely nested circular tubular members of the inner tubular members previously described and to reduce the corrective frontal area of the inner tubular members  54 . This honeycomb arrangement and each of its tubular members  54  completely define the open cross sectional area through which water must flow to propel the watercraft H. In this embodiment  50  the outer tubular member  52  also extends forwardly from the trailing edge of the propeller K and the forwardly planar surface of the inner tubular members  54 . 
   A mesh or screen  58  is positioned at the forwardly end of the tubular member  52  to prevent debris from striking the propeller K. The planar rearward surface  64  of the array of tubular members  54  is coplanar with the rearward end  60  of the outer tubular member  52 . Stabilizing and protective planes  62  are attached to and outwardly extending from the outer tubular member  52  for enhanced protection thereof from impact with ground or debris. 
   Referring now to  FIGS. 9 to 20 , various further embodiments of the invention are there shown. In  FIGS. 9 and 10 , the inner or central portion  76  of the inner tubular members is of a substantially smaller diameter than the array of inner tubular members  74  which extend around the inner periphery of the outer tubular member  72 . Again, in this embodiment  70 , the outer tubular member  72  extends forwardly of the planar forward surface  80  of the inner tubular member arrays for insuring that virtually all of the water flow created by the rotation of the propeller L extends rearwardly through the apparatus  70  in the direction of the arrow shown in hidden lines. 
   The embodiment  90  shown in  FIGS. 11 and 12  includes a dual diameter outer tubular member  92  having a larger diameter forwardly portion  92   a  sized to fit around the tips of the propeller M while the rearwardly portion transitions at  92   b  downwardly to a cylindrical smaller diameter  92   c . The inner tubular members  94  likewise transition in diameter from a larger diameter at  94   a  through the transitional diameter  94   b  to the smallest diameter at  94   c  to help create a vortex affect for enhanced water flow therethrough. 
   The opposite effect is created with the embodiment  110  in  FIGS. 13 and 14  wherein the outer tubular member  112  has a forwardly cylindrical portion  112   a  which is sized on its inner cylindrical surface to be just slightly larger than the diameter of propeller N. The central transitional portion  112   b  enlarges to the rearwardly portion  112   c  of the outer tubular member  112  to provide for reduced resistance to flow and to create a slight pressure gradient at surface  120 , the rearwardly planar surface of the inner tubular members  114 . 
   These inner tubular members  114  likewise transition at  114   b  forwardly portions  114   a  of the inner tubular members  114  which are of the smallest diameter while the central portion  114   b  expands to the largest rearward portion  114   c  of each of the tubular members  114 . Termination at the rearwardly planar surface  120  is coplanar with the rearwardly end of the outer tubular member  112 . 
   The embodiment  130  of  FIGS. 15 and 16  includes a cylindrical outer tubular member  132  sized to just fit around and forwardly extend around the outer diameter of propeller P. The diagonal leading edge  138  is provided for reduced water flow resistance of water entering into the open forwardly end of the tubular member  132 . In this embodiment  130 , the central array  136  of the inner tubular members is nested into a generally cylindrical central portion of tubular members  136  which are of a larger diameter while the tubular members  134  surrounding the larger inner tubular members  136  and fitting into and against the inner surface of the outer tubular member  132  are of a substantially smaller diameter. 
   In  FIGS. 17 and 18 , this embodiment  150  there shown includes a rearwardly tapering outer tubular member  152  which is sized at a forwardly leading edge  156  thereof to just fit around the tip of the blades of the propeller R. The inner tubular members  154  are uniformly sized and tapered so as to nest and be closely packed within the truncated conical inner surface of the inner tubular member  152  to create a nozzle effect. Again, the rearwardly plane  160  of the tubular members  154  is coplanar with the rearwardly end of the outer tubular member  152 . 
   In  FIGS. 19 and 20 , the embodiment  170  includes an outwardly tapering tubular member  172  which is sized at its forwardly cylindrical end  172   a  to just fit around and confine the tips of the propeller S so as to insure that all prop wash water flow flows into the leading surface  178  of the outwardly tapering plurality of tubular members  174 . The rearwardly surface of the plurality of outwardly tapering inner tubular members  174  is coplanar with the rearwardly end of the outer tubular member  172 . 
   Lastly, in  FIGS. 21 to 23 , yet another embodiment of the invention shown generally at numeral  190  is connected in transverse orientation through the lower bow area of the watercraft T. Again, a plurality of transversely oriented tightly nested inner tubular members  192  and  194  collectively define an outer tubular perimeter of this embodiment  190  transversely entirely through the bow. Side openings defined at  196  and  198  of the tubular members  192  and  194 , respectively, transverse water flow through this embodiment  190  in either direction shown in hidden lines depending upon the direction of rotation of the propeller V. The planes of the propeller V lie in close proximity to the inner orthogonal surfaces  200  and  202  of the inner tubular members  192  and  194 , respectively, to maximize the water flow straightening effect of this invention. 
   Note importantly that a wall thickness of the inner tubular members in all embodiments described is best selected to be as thin as possible and even sharpened at the leading or forwardly ends thereof to reduce resistance to water flow therethrough. Thus, minimizing the collective forwardly surface areas of the plurality of inner tubular members is of utmost importance. Tubular wall thicknesses of the inner tubular members which may be plastic or metal in the range of 0.03″ to 0.06″ in thickness is realistic when considering the collective strengthening and supporting effect of the closely nested inner tubular members within the outer tubular member inner surface thereof. 
   While the instant invention has been shown and described herein in what are conceived to be the most practical and preferred embodiments, it is recognized that departures may be made therefrom within the scope of the invention, which is therefore not to be limited to the details disclosed herein, but is to be afforded the full scope of the claims so as to embrace any and all equivalent apparatus and articles.