This gear box has a horizontal shaft which is balanced on one bearing on one side and a thrust bearing on the other side. The shaft is connected with the propeller on its end. This horizontal shaft has a back and forth movement which is actuated with the help of a solenoid or a mechanical lever. Figure. 1 Outboard engine Spur reduction gear box: This is a conventional gear box with two spur gears in contact with each other. The spur gears are designed to reduce the speed according to the RPM of the engine and the required RPM of the propeller.
The required RPM of the propeller is the Optimum design RPM at which the propeller is designed and results in highest efficiency. Reversible gear box: This is a bevel type gear box which changes the transmission to 90 degrees, i. e. vertical to horizontal. This receives the power form the vertical shaft and has a 45 deg bevel gear at its end. It is connected to the bevel gear on the horizontal shaft. The gear box has two bevel gears facing opposite to each other and they are connected to the horizontal shaft.
The vertical bevel is in between them and when the horizontal shaft slides back and forth with the help of a solenoid slider mechanism, it will be able to reverse the direction of motion. Horizontal shaft: The horizontal shaft is supported with a thrust block which restricts the horizontal movement of the inner shaft (the outer shaft slides and it changes the direction of rotation). The reaction force form the propeller thrust is absorber by the thrust block.
The other end is balanced by a plain bearing. The end of the shaft is sealed with water cooled white metal seals. This is a similar to ships stern tubing. This prevents the intrusion of water into the gearbox. The end of the shaft is screwed in the opposite direction of normal propulsion direction of rotation. This prevents the propeller from loosening when operating. The propeller boss is given internal threading and it is screwed at the end. The end is sealed with a bossing cover.