Water jacketed exhaust relief system for marine propulsion devices

Abstract

The outboard motor comprises a propulsion unit including an engine, an adaptor fixedly connected between the engine and a lower unit including an outer drive shaft housing, a gear case fixedly connected to the drive shaft housing and including a water discharge passage having a discharge port adapted to communicate with the water in which the lower unit is submerged for operation and an inner housing inside the drive shaft housing and spaced therefrom to define a lower unit water jacket and also defining an exhaust gas expansion chamber communicating with the engine exhaust. The inner housing includes a duct having an upper end communicating with the lower unit water jacket and into which overflow water from the lower unit water jacket is discharged and also having a lower end communicating with the gear case water discharge passage. A cover covering the engine and the adaptor includes a lower section having an exhaust gas discharge port which is located above the upper end of the drive shaft housing and which is connected in communication with the engine exhaust by a conduit including a portion of the inner housing extending downwardly to a location located below the upper end of the duct, at least one pocket on the interior of the inner housing and having an open upper end located above the upper end of the duct, an aperture in the inner housing connecting the interior of the pocket in communication with the lower unit water jacket at a location below the upper end of the duct, a passageway in the adaptor communicating with the lower unit water jacket, and a conduit connecting the adaptor passageway in communication and the exhaust gas discharge port.