Exhaust gas cleaning system for a marine propulsion unit

An exhaust gas cleaning system for use with a watercraft engine comprising a water cooled engine block and a cylinder head;

• and a plurality of exhaust ports located within said cylinder head, and positioned horizontally;
• and, an exhaust manifold in communication with each of said exhaust ports at a first end and forming a gas collecting pipe at a second end, said collecting pipe positioned above said exhaust ports;
• said exhaust manifold provided with a mating face which mates with said engine;
• said exhaust manifold further including a generally horizontally positioned exhaust pipe extending from said collecting pipe and continuing rearwardly therefrom;
• and means for introducing coolant from said engine into said rearwardly extending portion of said exhaust pipe;
• and, a catalyst member located within and across said horizontally positioned region of said exhaust pipe;
• said catalyst mounted within a catalyst holding structure formed within said exhaust pipe between said collecting pipe portion of said exhaust manifold and the area where coolant is introduced into said rearwardly extending portion of said exhaust pipe;
• and wherein said exhaust manifold is formed with an integral coolant jacket;
• and further comprising a coolant inlet provided substantially upstream of said catalyst holding structure for allowing coolant to enter said coolant jacket;
• wherein said coolant jacket is continuous and void of joints between said coolant inlet and a rearwardmost end of said catalyst;
• and wherein said catalyst is in a heat exchange relationship with said coolant jacket.