Marine propulsion and constructional details thereof

Abstract

A marine drive system mounted in the hull of a marine craft, the marine drive system comprising an engine connected to a gearbox by means of a drive shaft ( 532 ), a propeller ( 1 ) connected to the gearbox by means of a propeller shaft ( 501 ), wherein the gearbox and the propeller are formed as a single rigid body for flexibly mounting in the hull of the marine craft as a single unit, and wherein the engine, gearbox and propeller are positioned such that they are always generally aligned with the longitudinal axis of the craft.

1 . A marine drive system mounted in the hull of a marine craft, the marine drive system comprising:
 an engine connected to a gearbox by means of a drive shaft;   a propeller connected to the gearbox by means of a propeller shaft;   wherein the gearbox and the propeller are formed as a single rigid body for flexibly mounting in the hull of the marine craft as a single unit; and   wherein the engine, gearbox and propeller are positioned such that they are always generally aligned with the longitudinal axis of the craft.   
   
   
       2 . A marine drive system according to  claim 1 , wherein the gearbox is disposed remotely from the engine 
   
   
       3 . A marine drive system according to  claim 1 , further comprising a rigid frame connected between the gearbox and the craft. 
   
   
       4 . A marine drive system according to  claim 3 , wherein the drive shaft is formed from carbon fibre. 
   
   
       5 . A marine drive system according to  claim 1 , wherein the single rigid body comprises the engine, gearbox and propeller for mounting in the hull of a marine craft as a single unit. 
   
   
       6 . A marine drive system according to  claim 5 , wherein the engine and the gearbox are positioned adjacent to each other. 
   
   
       7 . A marine drive system according to  claim 1 , further comprising a second propeller connected to the gearbox by means of a second propeller shaft, the engine and the gearbox being aligned along the longitudinal axis of the craft and the propellers being aligned with the longitudinal axis of the craft. 
   
   
       8 . A marine drive system according to  claim 1 , further comprising a second single rigid body comprising a gearbox and a propeller; and
 wherein each single rigid body is generally aligned with the longitudinal axis of the craft.   
   
   
       9 . A marine drive system according to  claim 1 , wherein the ratio of the propeller diameter to the propeller shaft diameter is in the range of 4.5 to 5.5 
   
   
       10 . A marine drive system according to  claim 1 , wherein the ratio of the propeller shaft diameter to the propeller shaft length is in the range of 0.65 to 0.9. 
   
   
       11 . A marine drive system according to  claim 1 , wherein the gearbox has an input shaft driven by the engine and the ratio of the propeller shaft diameter to the input shaft diameter is in the range of 2.2 to 3.5. 
   
   
       12 . A marine drive system according to  claim 11 , wherein the ratio of the input shaft diameter to the input shaft length is in the range of 0.5 to 0.62. 
   
   
       13 . A marine drive system according to  claim 1 , wherein the single unit is provided with front mounting points adjacent to the engine and rear mounting points adjacent to the gearbox, for attaching to the hull of the marine craft. 
   
   
       14 . A marine drive system according to  claim 13 , wherein the rear mounting points are positioned at 8% to 12% of the overall length of the marine drive system from the centre of the propeller. 
   
   
       15 . A marine drive system according to  claim 13 , wherein the front mounting points are positioned at 40% to 60% of the overall length of the marine drive system from the rear mounts. 
   
   
       16 . A marine drive system according to  claim 1 , wherein the propeller is a surface-piercing propeller. 
   
   
       17 . A marine craft having a hull and a transom, the marine craft comprising a marine drive system comprising:
 an engine connected to a gearbox by means of a drive shaft;   a propeller connected to the gearbox by means of a propeller shaft;   wherein the gearbox and the propeller are formed as a single rigid body for flexibly mounting in the hull of the marine craft as a single unit; and   wherein the engine, gearbox and propeller are positioned such that they are always generally aligned with the longitudinal axis of the craft;   wherein the marine drive system is flexibly mounted to the hull of the marine craft.   
   
   
       18 . A marine craft according to  claim 13 , wherein the marine drive system is mounted to hull on front mounts and rear mounts;
 and the front mounts are arranged to take axial and lateral loads in addition to vertical loads; and   the rear mounts are arranged to take vertical and lateral loads and be compliant in the axial sense.   
   
   
       19 . A marine drive system according to  claim 1 , wherein the rotational axes of the drive shaft, the propeller shaft and the propeller are generally aligned with the longitudinal axis of the craft. 
   
   
       20 . A marine drive system according to  claim 1 , wherein any of the engines are provided with a structural sump or ladder frame to increase the bending stiffness of the engine and the stiffness of the connection between the engine and the gearbox. 
   
   
       21 . A marine drive system according to  claim 1 , wherein any of the propeller shafts are hollow.