Exhaust system for outboard motor

An outboard motor for attachment as a unit to the transom of a watercraft comprising:

• means for affixing said outboard motor unit to said transom;
• an engine having a horizontally disposed engine output shaft and at least one exhaust port disposed forwardly of said transom;
• a driveshaft housing disposed rearwardly of said transom and journaling a driveshaft for rotation about a generally vertically extending axis and driven by said output shaft;
• propulsion means at the lower end of said driveshaft housing and driven by said driveshaft for propelling the watercraft;
• a generally vertically extending expansion chamber formed in said driveshaft housing and having a horizontally extending med at the upper end of said expansion chamber and said driveshaft housing;
• and, exhaust means extending from said engine exhaust to said horizontally extending inlet for delivering exhaust gasses thereto, for expanding said exhaust gasses, and restricted exhaust gas discharge in the lower portion of said driveshaft housing for subsequently contracting exhaust gases before discharging to the atmosphere, through an underwater high speed exhaust discharge and low speed exhaust means, extending from said expansion chamber to the atmosphere above the water for cooling and expanding exhaust gases before discharging to the atmosphere.