Abstract: A number of embodiments of exhaust systems for outboard motors wherein the exhaust ports of the engine discharge the exhaust gases to the atmosphere through an underwater high speed exhaust gas discharge. A trap device is provided for precluding the water from the underwater exhaust gas discharge entering the engine through its exhaust ports. This trap device includes a section that extends above the highest exhaust port of the engine for this purpose.

Abstract: Two embodiments of outboard motors embodying tuned exhaust systems having exhaust pipes and expansion chambers into which the exhaust pipes extend. A catalyst is positioned in the exhaust system downstream of the point where the exhaust pipe terminates in the expansion chamber so as to preclude interference with the exhaust tuning. The catalyst bed is removable for ease of servicing without necessitating removal of the outboard motor from the its attachment to the associated watercraft and a trap device is provided for precluding water from entering the engine through its exhaust ports.