Exhaust system for outboard marine propulsion unit

Claim 1

Outboard marine propulsion unit comprising an internal combustion engine unit having exhaust port means, housing means supporting said engine unit and adapted to be mounted on a body of a boat, propulsion means mounted on said housing and being driven by said engine unit through drive shaft means, said housing means having a top end and an inner wall surface defining hollow chamber means extending downwardly from the said top end of the housing means and having outlet port means, engine exhaust pipe means having one end connected with said exhaust port means of the engine unit and being projected into said chamber means in the housing means, said exhaust pipe means being formed with at least one radially outwardly extending partition wall for dividing said hollow chamber means into at least two compartments which are connected together through restricted passage means defined by the clearance between said outwardly extending partition wall and said inner wall surface, whereby engine exhaust gas is directed from the exhaust pipe means through one of the compartments, the restricted passage means and the other of the compartments to the outlet port means.