Abstract: An exhaust-through-the-hub system described herein includes an apparatus for discharge of exhaust gases from a marine outboard motor to the outer perimeter of an attached pump jet. Exhaust gas is ducted downwardly through the central body of the motor and rearwardly into a plenum cavity positioned in the pump jet. At least one hollow stator vane receives the exhaust gas and discharges the exhaust gas through the stator housing at a substantial depth below the water line, thereby resulting in a quieter running engine. The exhaust-through-the-hub system provides forward thrust when the motor is in forward gear and reverse thrust when the motor is in reverse gear.

Abstract: A marine pump jet apparatus is described which is attached to the lower unit of a conventional outboard motor. The pump jet, which replaces the usual propeller element, consists of an axial flow pump containing a bladed impeller and stator vanes enclosed in a housing. In conventional outboards, exhaust gas flows downward from the power head through a duct in the motor and rearward through ducts in the motor gear case and the propeller hub to be discharged under water. In the present apparatus, before the exhaust reaches the gearcase, it is directed into a diversion passage which causes it to exit (still under water) above the upper surface of the pump jet. A trough is provided in the upper surface of the pump jet housing. The diversion passage directs a portion of the exhaust stream into the trough, thereby reducing drag on the motor.