Exhaust arrangements for marine propulsion devices

A marine propulsion device comprising:

• an internal combustion engine that discharges exhaust gases;
• a driveshaft housing that is located vertically below the internal combustion engine;
• and
• a catalyst that is sandwiched between water-cooled opposing castings of the internal combustion engine that face each other at a split-line;
• wherein the exhaust gases flow through the catalyst parallel to the split-line;
• and
• wherein the water-cooled opposing castings of the internal combustion engine define cavities that are sized and shaped so that the catalyst is radially compressed by the water-cooled opposing castings when the water-cooled opposing castings are fixed together.

A marine propulsion device comprising:

• an internal combustion engine that discharges exhaust gases;
• a driveshaft housing that is located vertically below the internal combustion engine;
• a catalyst that is sandwiched between opposing castings of the internal combustion engine that face each other at a split-line;
• wherein the exhaust gases flow through the catalyst parallel to the split-line;
• wherein the opposing castings of the internal combustion engine define cavities that are sized and shaped so that the catalyst is radially compressed by the opposing castings when the opposing castings are fixed together;
• wherein the catalyst extends between first and second ends;
• and
• at least one circumferential protuberance on each of the first and second ends of the catalyst, wherein each protuberance separates the catalyst from the opposing castings of the internal combustion engine so as to define an air gap therebetween;
• wherein each protuberance forms a circumferential seal with the opposing castings of the internal combustion engine;
• wherein the circumferential seal prevents exhaust gases from bypassing the catalyst;
• and
• wherein each protuberance transfers radial pressure from the opposing castings to the catalyst to thereby retain the catalyst in place.