Propulsion unit for motor boats

Abstract

A propulsion unit for motor boats is disclosed, wherein a drive member is assembled within the hull bottom, in proximity of the transom and drives at least one propeller having a large-diameter hub and being placed outside the hull in proximity of the transom.

1 . A propulsion unit for boats, comprising at least one engine and at least one reversing gearbox that are housed within the hull of a boat, and at least one propeller which is driven by said engine and placed outside the hull of said boat, characterized by comprising at least one drive member that is assembled within the bottom of said hull in proximity of the transom and having at least one output shaft with at least one propeller adjusted thereon, and said at least one propeller being assembled in proximity of the transom of said hull, the hub of said at least one propeller having a radius substantially equal to the distance between the axis of said at least one output shaft and the outer wall of the bottom of said hull.  
   
   
       2 . The propulsion unit according to  claim 1 , wherein the axis of said at least one output shaft is substantially parallel to the waterline of the boat.  
   
   
       3 . The propulsion unit according to  claim 1 , wherein the inclination of the axis of said at least one output shaft relative to the waterline of the boat ranges between 0° and 4°.  
   
   
       4 . The propulsion unit according to  claim 1 , wherein said drive member is assembled close to the transom of said hull.  
   
   
       5 . The propulsion unit according to  claim 1 , wherein said drive member comprises at least one power takeoff that is substantially parallel to the axis of said output shaft.  
   
   
       6 . The propulsion unit according to  claim 1 , wherein said drive member comprises at least one power takeoff that is substantially co-axial with the axis of said output shaft.  
   
   
       7 . The propulsion unit according to  claim 1 , wherein said drive member is a gear drive member and comprises at least two co-axial output shafts of which at least one is hollow and houses the other therein, and wherein one or more gears are provided in order to rotate said co-axial output shafts in mutually opposite direction.  
   
   
       8 . The propulsion unit according to  claim 7 , wherein at least one propeller is provided which is mounted at the end of each of said co-axial output shafts, and wherein the hub of said propellers has a radius substantially equal to the distance between the axis of said co-axial output shafts and the outer wall of the bottom of said hull.  
   
   
       9 . The propulsion unit according to  claim 7 , wherein a first of said propellers is mounted in proximity of the transom and is adjusted to the end of the outer co-axial output shaft and a second one of said propellers is assembled in proximity of said first propeller and adjusted to the end of the inner co-axial output shaft.  
   
   
       10 . The propulsion unit according to  claim 7 , wherein said gear drive member comprises different gear ratios between said two output shafts.  
   
   
       11 . The propulsion unit according to  claim 7 , wherein said co-axial output shafts are supported with friction-reducing means.  
   
   
       12 . The propulsion unit according to  claim 11 , wherein said friction-reducing means include one or more bearings.  
   
   
       13 . The propulsion unit according to  claim 11 , wherein said friction-reducing means include one or more bushes with dynamic water-lubrication.  
   
   
       14 . The propulsion unit according to  claim 1 , wherein said drive member comprises an outer envelope that is provided with a mounting section suitable to be fitted in a through hole of the transom.  
   
   
       15 . The propulsion unit according to  claim 14 , wherein the substantially cylindrical mounting section of the envelope of said drive member comprises one or more seats to hold one or more sealing elastic members in position between said mounting section and said hole of the transom.  
   
   
       16 . The propulsion unit according to  claim 1 , wherein said drive member comprises an outer envelope that is provided with a substantially spherical mounting section suitable to be housed in a correspondingly shaped and sized seat.  
   
   
       17 . The propulsion unit according to  claim 16 , wherein said spherical seat housing said spherical mounting section includes one or more flanges being fixed to the transom of the boat.  
   
   
       18 . The propulsion unit according to  claim 1 , wherein said reversing gearbox is integrated in said gear drive member.  
   
   
       19 . The propulsion unit according to  claim 1 , wherein means are provided in order to change, in a controlled manner, the inclination of the axis of said at least one output shaft relative to the waterline of the boat by an amount ranging between 0° and 4°.  
   
   
       20 . The propulsion unit according to  claim 19 , wherein said drive member comprises a control piston in order to change the inclination of the propeller axis relative to the waterline.  
   
   
       21 . A motor boat, characterized by comprising a propulsion unit according to  claim 1 .  
   
   
       22 . The motor boat according to  claim 21 , wherein said propulsion unit is applied to a transmission with reversing gearbox directly fixed to the propulsion unit.  
   
   
       23 . The motor boat according to  claim 21 , wherein said propulsion unit is applied to a V-Drive transmission with engine and reversing gearbox being arranged above the propeller axis.  
   
   
       24 . The motor boat according to  claim 21 , wherein said propulsion unit is applied to a Ring-Drive transmission with engine being supported by said propulsion unit.  
   
   
       25 . The motor boat according to  claim 21 , wherein the hull is a mono-hull or catamaran, either planing or displacement hull.  
   
   
       26 . The motor boat according to  claim 21 , wherein means are provided to suck the air in the vicinity of said propellers above the water line to avoid the phenomenon of cavitation.