Wake adapted propeller drive mechanism for delaying or reducing cavitation

Abstract

A wake adapted propeller drive mechanism delays or reduces cavitation or stall in a propeller drive mechanism mounted for rotation at the stern of a hull so as to be rotatable in a wake produced by forward motion of the hull through the water. The wake adapted propeller drive mechanism skews the drive shaft of the propeller sideways of the hull in a horizontal plane so as to adjust the angles of attack of the propeller to maintain the angles of attack below that which could produce cavitation or cavitation noise.

1 . A wake adapted propeller drive mechanism for delaying or reducing cavitation, said mechanism comprising, 
 a hull having a bow and a stern,    a wake adapted propeller having multiple, identically configured blades extending radially from a hub and mounted for rotation at the stern of the hull so as to be rotatable in a wake produced by the forward motion of the hull through the water, and    wherein, for said propeller mounted for rotation in a plane aligned perpendicular to the axis of flow of the wake, the angle of attack of a cross section of a propeller blade must be below a certain upper limit in order to avoid, in at least certain critical radial portions, cavitation and cavitation noise, stall and loss of lift as the cross section is rotated through the wake,    said mechanism including mounting means which mount said wake adapted propeller for rotation in a plane that is inclined to the axis of flow of the wake and which skews the drive shaft of the wake adapted propeller sideways of the hull in a horizontal plane, and    wherein the angles of attack of the blade cross sections on said wake adapted propeller are adjusted, by said skew of the drive shaft, to be below said upper limits for corresponding radial portions of said conventional propeller so as not to produce cavitation or cavitation noise, or stall and loss of lift.    
     
     
         2 . The mechanism defined in  claim 1  wherein the amount of said skew is effective to prevent any cavitation in any part of the wake until the angles of attack produce incipient cavitation at other portions in the rotation of said wake adapted propeller through the wake.  
     
     
         3 . A wake adapted propeller drive mechanism for delaying or reducing cavitation, said mechanism comprising, 
 a symmetrical hull having a bow and a stern,    a strut connected to the top of the hull and holding the hull submerged in the water beneath a water craft superstructure,    a wake adapted propeller having multiple, identical configured blades extending radially from a hub and mounted for rotation at the stern of the hull so as to be rotatable, at least in part, in both a wake produced by the forward motion of the submerged hull through the water and in a deficit, upper portion of the wake, and    wherein, for said propeller mounted for rotation in a plane aligned perpendicular to the axis of flow of the wake, the angle of attack of a cross section of a propeller blade must be below a certain upper limit in order to avoid, in at least certain critical radial portions, cavitation and cavitation noise, stall and loss of lift as the cross section is rotated through the deficit portion of the wake,    said mechanism including mounting means which mount said wake adapted propeller for rotation in a plane that is inclined to the axis of flow of the wake and which skews the drive shaft of the wake adapted propeller sideways of the hull in a horizontal plane, and    wherein the angles of attack of the blade cross sections on said wake adapted propeller are adjusted by said skew of the drive shaft to be below said upper limits for corresponding radial portions of said conventional propeller so as not to produce cavitation or cavitation noise.    
     
     
         4 . The mechanism defined in  claim 3  wherein the cross sections of a blade of said wake adapted propeller in the various radial portions of the blade are constructed according to a design having a pressure distribution lower than the cavitation limit along the entire length of the blade to have an adjusted angle of attack which delays cavitation at each cross section until the inception of cavitation of the entire blade as it rotates all the way around and through the wake.  
     
     
         5 . The mechanism defined in  claim 3  wherein the adjusted angles of attack of the cross sections of the blades of said wake adapted propeller are enough greater, in the lower half portion of the wake, than the effective angles of attack of the conventional propeller to produce a substantial increase in propulsion efficiency of the wake adapted propeller.  
     
     
         6 . The mechanism defined in  claim 3  wherein the strut slows the inflow velocity to said wake adapted propeller in the deficit, upper portion of the wake and wherein the amount of skew of the drive shaft adjust said angles of attack so as to be ninety degrees out of phase with the decrease in the inflow velocity caused by the strut.  
     
     
         7 . The mechanism defined in  claim 3  wherein the adjusted angles of attack of the cross sections of the blades of said wake adapted propeller are reduced enough, in the deficit portion of the wake, to prevent inception of cavitation or stall as it rotates through the deficit portion of the wake.