Twin-propeller drive for watercraft

Abstract

Dual propeller propulsion system for water crafts having two propellers (3, 4) fitted in the same axis outside the ends of an underwater housing (2) configured as a gondola so as to facilitate flow, said housing being placed under the hull of the water craft having a driving mechanism lodged in the underwater housing for both propellers (3, 4) to which the energy coming out for both propellers (3, 4) to which the energy coming out of the hull of the water craft is guided by means of a housing shank (18), one of the ends of which is mounted on the hull (24) of the water craft while the other is mounted in the underwater housing (2). Said propulsion system is characterized in that the underwater housing (2) forms part of a control device (20) by means of which the water jet coming out with increased energy from the front propeller (3) in the direction of travel of the water craft is guided with minimal energy loss and optimal irrotational flow to the back propeller (4) placed in the other end of the underwater housing in the direction of travel of the water craft. Both propellers (3, 4) are driven by the driving mechanism placed in the underwater housing in the same direction of rotation and are configured in the area of the respective water jet cross section in such a way that the differing flow energy entering both propellers (3, 4) is optimally used.

What is claimed is:  
     
         1 . A watercraft drive for a watercraft having a hull, said watercraft drive comprising, 
 drive means including a motor having two drive shafts, and front and rear propellers respectively mounted on said drive shafts in coaxial longitudinally displaced relationship, each of said propellers having at least two blades,    control means disposed between said front and rear propellers, for increasing the energy of a jet of water exiting the front propeller as said jet is transmitted to the rear propeller, said control means causing the water jet leaving the front propeller with a contracted cross-section and both circular and axial flow components to reach the rear propeller substantially without circular components, said front and rear propellers having equal diameters and being driven at like rotational velocities,    said rear propeller having a core area conforming with the cross section of the contracted cross section of the jet leaving the front propeller, the geometry of the blades of the rear propeller being optimized for an incoming jet energy substantially equal to the exit energy of the jet exiting the front propeller,    said rear propeller further having an annular area extending from said core area to a circular path defined by an outer circumference of the rear propeller, the geometry of the blades in said annular area conforming to the geometry of the blades of the front propeller, said annular area of the rear propeller receiving a flow of surrounding ambient water,    said control means comprising, a hollow shaft having an upper end connected to said hull, and a lower end, a gondola-shaped underwater housing mounted on the lower end of said hollow shaft and containing said drive means, said drive shafts extending from opposite ends of said housing, and a plurality of guide blades connected to at least one of said hollow shaft and gondola-shaped underwater housing,    power means mounted in said hull for transmitting power through said hollow shaft to said drive means for rotating said front and rear propellers,    said motor having a rotor covered by a motor housing, said motor housing being connected, in heat conducting relationship to the inside wall of said underwater housing, whereby heat from said motor is transferred to water surrounding said shaft and said underwater housing.    
     
     
         2 . A watercraft drive in accordance with    claim 1   , wherein the pitch of the blades in the core area of the rear propeller is 1.04 to 1.52 times the pitch of the blades in the core area of the front propeller.  
     
     
         3 . A watercraft drive in accordance with    claim 2   , wherein the pitch of the blades in the annular area of the front propeller is between 95 percent and 105 percent of the pitch of the blades in the annular area of the rear propeller.  
     
     
         4 . A watercraft drive in accordance with    claim 2    wherein the pitches of the blades of each of the front and rear propellers is in the range of 0.9 to 1.6.  
     
     
         5 . A watercraft drive in accordance with    claim 2    wherein the blades of the front and rear propellers have different degrees of arcing.  
     
     
         6 . A watercraft drive in accordance with    claim 1    wherein said guide blades which have an arc length ratio in the range of 0.0 to 0.2 and an angle of incidence in the range of −7 to +7.  
     
     
         7 . A watercraft drive in accordance with    claim 6   , wherein the control device has two guide blades which are angularly symmetrically disposed about the common axis of rotation of the front and rear propellers.  
     
     
         8 . A watercraft drive in accordance with    claim 1    wherein the drive means further comprises a transmission, said drive shafts extending from opposite ends thereof, and a connection shaft extending from said transmission through said hollow shaft into said hull for connection to an engine disposed therein.  
     
     
         9 . A watercraft drive in accordance with    claim 1    further comprising a plurality of electrical conductors extending from said motor through said hollow shaft into said hull for connection to a source of electrical power therein.  
     
     
         10 . A watercraft drive in accordance with    claim 1    wherein said motor comprises a hydraulic engine operatively connected to hydraulic fluid lines extending through said hollow shaft into said hull for connection to a source of hydraulic power.  
     
     
         11 . A watercraft drive in accordance with    claim 1    further comprising an accelerating nozzle jacketing the front propeller, said accelerating nozzle having a cross section which tapers from an inlet end upstream of the front propeller to a plane of rotation of the front propeller.  
     
     
         12 . A watercraft drive in accordance with    claim 1    wherein each of said front and rear propellers is jacketed by a decelerating nozzle having a cross section which increases from a respective nozzle inlet to a plane of rotation of the respective propeller.  
     
     
         13 . A watercraft drive in accordance with    claim 1   , wherein the upper end of the hollow shaft is rotatably mounted on the hull for enabling rotation of the underwater housing relative to the hull.  
     
     
         14 . A watercraft drive in accordance with    claim 13   , wherein the hollow shaft is rotatable about a longitudinal axis relative to the hull by 360 degrees.  
     
     
         15 . A watercraft drive in accordance with    claim 1    further comprising a front hub for fastening the front propeller to its respective drive shaft and a rear hub for fastening the rear propeller to its respective drive shaft, the front hub and rear hub being contoured for enhancing flow from the front propeller to the rear propeller.  
     
     
         16 . A watercraft drive in accordance with    claim 1    wherein the motor is a permanently excited synchronous electric motor.  
     
     
         17 . A watercraft drive in accordance with    claim 16    further comprising clutch means for connecting said driving shafts to said rotor, said driving shafts passing concentrically through the rotor and extending from both ends of the rotor for receiving the propellers which rotate in unison with said driving shaft.  
     
     
         18 . A watercraft drive in accordance with    claim 17    further comprising bearing means operatively mounted between said housing and said rotor.  
     
     
         19 . A watercraft drive in accordance with    claim 1    further comprising rotor support tube means for coupling said drive shaft and said rotor.  
     
     
         20 . A watercraft drive in accordance with    claim 17    wherein the axis of the hollow shaft intersects and is orthogonal to the axis of the drive shaft, and further comprising a carrier cone to which the upper end of the hollow shaft is connected, the housing being continuously pivotable by 360 degrees around the longitudinal axis of the hollow shaft.  
     
     
         21 . A watercraft drive in accordance with    claim 20   , wherein the hollow shaft and the carrier cone are mutually detachably connected in a plane of the hull.  
     
     
         22 . A watercraft drive in accordance with    claim 20    wherein the carrier cone has a large end and a small end having a smaller cross section than said large end, the hollow shaft being connected to the small end of the carrier cone and the large end of the carrier cone being connected to the watercraft within the hull.  
     
     
         23 . A watercraft drive in accordance with    claim 7    wherein the hollow shaft comprises one of said guide blades which are rotationally symmetrical disposed about the common axis of rotation of the front and rear propellers.  
     
     
         24 . A watercraft drive in accordance with    claim 1    wherein the front propeller is jacketed by a decelerating nozzle having an inlet and a cross section which increases from the inlet to the plane of rotation of the propeller.  
     
     
         25 . A watercraft drive in accordance with    claim 1    wherein each of the front and rear propeller is jacketed by one of an accelerating nozzle having an inlet and a cross section that decreases with distance from its inlet to the plane of rotation of its respective propeller, and a decelerating nozzle having an inlet and a cross section that increases from its inlet to the plane of rotation of its respective propeller.  
     
     
         26 . A watercraft drive in accordance with    claim 1    wherein each of the front and rear propellers is surrounded either one of an accelerating nozzle having an inlet and a cross section decreasing with distance from the inlet of the nozzle toward the plane of rotation of the first propeller, and a decelerating nozzle having a cross section increasing with distance from the inlet of the nozzle toward the plane of rotation of the first propeller.  
     
     
         27 . A watercraft drive in accordance with    claim 1    wherein said motor is an electric motor having a rotor and a stator and further comprising, 
 a first support tube connected in heat conducting relationship to said rotor,  
 a second support tube having an inner surface connected in heat conducting relationship to said stator and an outer surface connected in heat conducting relationship to said underwater housing,  
 means for connecting said shafts to said first support tube,  
 a plurality of flanges connected in heat conducting relationship to said underwater housing, and  
 bearing means operatively connected between said first support tube and said flanges, whereby heat from said rotor and stator is conducted to ambient water surrounding said underwater housing and shaft for cooling said motor.