A number of embodiments of exhaust silencers for marine propulsion units including an exhaust device having a first expansion chamber, a pair of second expansion chambers and a third expansion chamber all formed within a common housing. The flow of exhaust gases is from the exhaust of the engine into the first expansion chamber, directly from the first expansion chamber into each of the pair of second expansion chambers and directly from the second expansion chambers to the third expansion chamber. In all embodiments the flow from the second expansion chambers to the third expansion chamber is in confronting relationships so as to improve silencing. In one embodiment, the second expansion chambers have different effective volumes so as to provide an extended range of tuning for the silencing.