Abstract: An exhaust system for a marine engine comprising liquid-cooled manifold and catalytic converter assemblies. Each assembly uses a separate cooling system to cool either the exhaust manifold or a shell inside which resides the catalytic converter. The housing or shell containing the catalytic converter uses water to cool an exterior surface of a water jacket to an acceptable temperature conforming to federal regulations. The liquid-cooled manifold assembly may use either water or glycol to cool outer cooling tubes surrounding exhaust tubes extending from the engine block to the catalytic converter assembly.

Abstract: An exhaust system for a in e engine comprising liquid-cooled manifold and catalytic converter assemblies. Each assembly uses a separate cooling system to cool either the exhaust manifold or a shell inside which resides the catalytic converter. The housing or shell containing the catalytic converter uses water to cool an exterior surface of a water jacket to an acceptable temperature conforming to federal regulations. The liquid-cooled manifold assembly may use either water or glycol to cool outer cooling tubes surrounding exhaust tubes extending from the engine block to the catalytic converter assembly.

Abstract: A marine propulsion system, preferably having dual counterrotating propellers, has an automatic multi-speed shifting mechanism such as a transmission. An electronic controller monitors engine parameters such as engine revolution speed and load, and generates a control signal in response thereto, which is used to control shifting. Engine load is preferably monitored by sensing engine manifold air pressure. The electronic controller preferably has a shift parameter matrix stored within a programmable memory for comparing engine speed and engine load data to generate the control signal. The system can also have a manual override switch to override shifting of the shifting mechanism.