Marine drive transmission with contra-rotating propellers

Abstract

A marine drive assembly has a housing extending along a central axis and defining a gearbox section and a driveshaft section. A bevel gear assembly is housed in the gearbox section and has a first bevel gear rotatable about a central axis, a second bevel gear rotatable about the central axis, and a third bevel gear rotatable about a radial axis and operatively engaging the first bevel gear and the second bevel gear. A mounting flange is connected to and extends around at least part of the gearbox section. An inner shaft extends along the central axis and is operably connected to the first bevel gear for rotation in a first rotational direction about the central axis. An outer shaft is coaxially arranged with the inner shaft and operably connected to the second bevel gear for rotation in an opposite second rotational direction about the central axis.

1 . A marine drive assembly, comprising:
 a housing extending along a central axis and defining a gearbox section and a driveshaft section;   a bevel gear assembly housed in the gearbox section and having a first bevel gear rotatable about a central axis, a second bevel gear rotatable about the central axis, and a third bevel gear rotatable about a radial axis and operatively engaging the first bevel gear and the second bevel gear;   a mounting flange connected to and extending around at least part of the gearbox section;   an inner shaft extending along the central axis and operably connected to the first bevel gear for rotation in a first rotational direction about the central axis; and   an outer shaft coaxially arranged with the inner shaft and operably connected to the second bevel gear for rotation in an opposite second rotational direction about the central axis.   
     
     
         2 . The marine drive assembly of  claim 1 , wherein a majority portion of the bevel gear assembly is above the mounting flange. 
     
     
         3 . The marine drive assembly of  claim 1 , further comprising a first propeller attached to the inner shaft and a second propeller attached to the outer shaft, wherein during use the first propeller rotates in a first rotational direction and the second propeller rotates in an opposite second rotational direction about the central axis. 
     
     
         4 . The marine drive assembly of  claim 1 , wherein the central axis defines an angle from 15-25° with a top surface of the flange. 
     
     
         5 . The marine drive assembly of  claim 1 , further comprising a skeg attached to the driveshaft section of the housing. 
     
     
         6 . The marine drive assembly of  claim 5 , wherein the skeg is removably attached to the driveshaft section. 
     
     
         7 . The marine drive assembly of  claim 1 , wherein the housing lacks a strut. 
     
     
         8 . The marine drive assembly of  claim 1 , wherein the inner shaft defines a helical groove. 
     
     
         9 . The marine drive assembly of  claim 1 , wherein the first bevel gear is a drive gear. 
     
     
         10 . The marine drive assembly of  claim 1 , wherein the mounting flange extends around a lower and aft portion of the gearbox section. 
     
     
         11 . The marine drive assembly of  claim 10 , wherein the mounting flange has a width less than 300 mm and a length less than 500 mm. 
     
     
         12 . The marine drive assembly of  claim 1 , wherein the driveshaft section has an outer diameter of less than 100 mm. 
     
     
         13 . The marine drive assembly of  claim 12 , wherein the gearbox section has an outer diameter of less than 150 mm. 
     
     
         14 . A boat having a hull and comprising:
 the marine drive assembly of  claim 1 ;   an inboard motor in the hull;   a drive shaft operably coupled to the inboard motor extending rearward from the inboard motor to the marine drive assembly.   
     
     
         15 . The boat of  claim 14 , wherein the hull defines a bottom recess and the wherein mounting flange extends around an outside of the bottom recess.