Marine propulsion unit

An outboard motor for attachment to the transom of a hull of an associated watercraft for powering said watercraft, said outboard motor being comprised of a power head comprised of a powering internal combustion engine having at least one exhaust port and a surrounding protective cowling, a lower unit depending from said power head and carrying a propulsion device powered by said internal combustion engine for providing a propulsion thrust to the associated watercraft, at least the lower portion of said power head comprised of the lower portion of the protective cowling and a buoyant body contained within said protective cowling and upon which said engine is mounted being water tight and buoyant, said buoyant body defining an expansion chamber volume to which exhaust gases are delivered from said engine exhaust port for silencing said exhaust gases and adding to the buoyancy of said buoyant body, and means for mounting said outboard motor upon said transom with said lower portion of said power head including the buoyant body but not said engine being at least partially submerged when said watercraft is in a body of water and not in a planing condition and completely out of the water when said watercraft is in planing condition.